Chrystia Freeland, Canada’s former deputy prime minister, whose sudden resignation in December helped set the stage for Prime Minister Justin Trudeau’s decision to step down, said on Friday that she was running to replace him.

She posted her announcement on X with a six-word sentence: “I’m running to fight for Canada.”

Ms. Freeland, 56, once a close ally of Mr. Trudeau who was often called his “minister of everything,” had served as deputy prime minister since 2019, and had long been viewed as a possible successor.

But the two had a bitter rift when Mr. Trudeau moved to demote her over a Zoom call in December, offering her a minister-without-portfolio role. Instead, she opted to resign and delivered a strong rebuke of Mr. Trudeau’s leadership as Canada prepares to deal with President-elect Donald J. Trump. Mr. Trump has threatened to apply a tariff on Canadian exports to the United States.

Her stinging departure destabilized Mr. Trudeau’s shaky grip on power. Three weeks later, on Jan. 6, he announced he would step down as Liberal Party leader and as prime minister once a new leader was in place.

Candidates for the leadership post will campaign ahead a national vote among party members in March. The new Liberal Party leader will also become Prime Minister of Canada and lead the party in a general election expected to take place in the spring.

Ms. Freeland said she would officially launch her campaign in person on Sunday, which could take place in Toronto, the electoral district she represents in parliament. She will face a stiff challenge persuading Canadians that she is the candidate best suited to take on the Conservative Party and its leader, Pierre Poilievre.

The Conservatives, who have a 25 percentage point lead over the Liberals in polls, have sought to portray Ms. Freeland as part of the problem given her once-close relationship with Mr. Trudeau and her key role in his governments since 2015, when he first became prime minister.

Mr. Trudeau’s popularity has nose dived in recent years as Canadians have become increasingly frustrated with persistently high cost-of-living on everything from housing to grocery bills.

Many Canadians have also started pushing back against the government’s immigration policy, which has resulted in 2.3 million people arriving in the country in the past two years. While the government said migrants were necessary to help fill gaps in low-skilled jobs, many Canadians say the new arrivals have contributed to rising housing costs and strains on the public health care system.

Ms. Freeland had accused Mr. Trudeau of engaging in political gimmickry after her ministry clashed with his office about a temporary sales-tax break during the end-of-year holidays.

The government estimated that the tax break, which covered items like restaurant bills and some toys and clothing, would cost about 1.6 billion Canadian dollars, or $1.1 billion, which Ms. Freeland said that Canada could “ill afford” at a time when Mr. Trump is raising the specter of tariffs.

“We need to take that threat extremely seriously,” Ms. Freeland said in her resignation letter. “That means keeping our fiscal powder dry today, so we have the reserves we may need for a coming tariff war.”

Ms. Freeland was born and raised in Alberta and is of Ukrainian ancestry. She has been a staunch supporter of Ukraine on the global stage, denouncing Russia’s invasion.

She attended Oxford University as a Rhodes Scholar, and worked as a journalist and newsroom leader at a number of news organizations, including the Financial Times and Reuters, before joining the Liberal Party in 2013. She is married to a reporter on the Culture desk of The New York Times and has three children.

During Mr. Trump’s first term, Ms. Freeland steered Canada’s renegotiation of the North American Free Trade Agreement with the United States and Mexico, portraying steely confidence during the tense talks with the odd moment of levity. (Ms. Freeland was photographed arriving in Washington in 2018 wearing a white T-shirt that read “Keep Calm and Negotiate NAFTA.”)

But she also angered Mr. Trump during the negotiations and his animosity has apparently not waned.

When Ms. Freeland resigned in December, Mr. Trump posted triumphantly: “Her behavior was totally toxic, and not at all conducive to making deals which are good for the very unhappy citizens of Canada. She will not be missed!!!”

Ms. Freeland, in an opinion piece published on Friday, hinted that Canada would retaliate in “the single largest trade blow the U.S. economy has ever endured.”

As finance minister, she spearheaded popular government programs to reduce the cost of day care for parents and to tackle childhood poverty.

Her announcement on Friday marks the second entry of a top contender in the Liberal Party leadership race. She will face off against Mark Carney, a former head of the central banks in Canada and England, who declared he was running on Thursday.

Mr. Carney is close friends with Ms. Freeland and is the godfather to one of her three children. He was being recruited by Mr. Trudeau’s team to take Ms. Freeland’s place in the government in December, but declined the job.

Donald Trump has promised to pursue the largest deportation operation in American history as soon as he takes office.

But the Mexican government and other regional allies have been unable to meet with the incoming Trump administration, according to officials in Latin America, leaving them in the dark about the president-elect’s plans to deport millions of illegal immigrants.

The incoming administration rebuffed requests by Mexico for a formal meeting, insisting that detailed discussions will only begin after Mr. Trump is sworn in next Monday, according to a Mexican official and two people familiar with the exchanges who were not authorized to speak publicly.

The Guatemalan and Honduran governments received similar messages, according to officials from those countries.

“This is not the way things usually work,” said Eric L. Olson, a fellow at the Wilson Center’s Latin American program and Mexico Institute. “Usually there are more informal contacts and some level of discussion by now.”

The incoming administration may want to limit confrontation before ramping up pressure by signing a flurry of executive orders on migration, analysts say, leaving governments in the region scrambling to respond. That would likely strengthen Washington’s hand in upcoming negotiations.

“At the moment, we cannot talk about concrete measures because we have not had any specific conversations about immigration policies with the incoming authorities,” Santiago Palomo, the spokesman for Guatemala’s president, said in an interview about how his country is preparing to respond to Mr. Trump’s mass deportation plans.

Guatemala’s ambassador to the United States was in touch with the Trump transition team, officials said, but members of the incoming administration had not communicated specific plans around a ramp-up in deportations, or how Guatemala should prepare.

Honduran government officials also said they had not yet had significant contact with the incoming Trump administration. Earlier this month, President Xiomara Castro of Honduras threatened to push the U.S. military out of a base it built decades ago in the Central American country if Mr. Trump carries out mass deportations.

Given Mr. Trump’s sharp focus on Latin America, the lack of clarity on his objectives has rattled regional governments.

The incoming administration has said that it wants to restore the “Remain in Mexico” policy implemented during the first Trump term, which forces some migrants to wait in Mexico rather than in the United States while their asylum cases are pending. Mr. Trump has also said he intends to declare a national emergency and use the U.S. military in some form to assist in his plans for mass deportations of millions of undocumented immigrants.

“President Trump will enlist every federal power and coordinate with state authorities to institute the largest deportation operation of illegal criminals, drug dealers and human traffickers in American history,” Karoline Leavitt, a spokeswoman for the Trump transition team, wrote in an email to The New York Times. She did not respond to questions about whether the incoming administration has rebuffed Mexico’s and other countries’ requests for meetings.

Mexico’s new president, Claudia Sheinbaum, has said her administration does not approve of the mass deportation program. “Of course, we do not agree,” she said in a news conference on Wednesday. “But, in the event of such a decision by the U.S. government, we are prepared.”

But whenever asked how the country will respond, her answers have been evasive — although she recently signaled the country’s willingness to accept some non-Mexican deportees.

“We are going to ask the United States that, as far as possible, the migrants who are not from Mexico can be sent to their countries of origin — and if not, we can collaborate through different mechanisms,” she told reporters earlier this month.

Some analysts said Mr. Trump’s team may be limiting their meetings with Latin American governments because they are worried about violating the Logan Act. That law forces incoming administrations to limit the scope of their negotiations with foreign governments until they take office, so as not to undermine sitting American presidents.

But previous incoming administrations have met with foreign governments to cautiously discuss their policy objectives, without violating the act.

Either way, the act has done little to curb Mr. Trump’s appetite to meet with his future counterparts. Since his November election, Mr. Trump has met separately with the leaders of Italy, Canada and Argentina at his hotel in Mar-a-Lago.

Despite the lack of contact, Mr. Trump has made his foreign policy objectives clear through speeches and on social media, giving the Mexican and other regional governments some insight into potential U.S. policies in the pipeline.

“Trump has signaled publicly that migration is a top priority, as are tariffs,” Mr. Olson said.

Shortly after his electoral victory, Mr. Trump threatened to slap 25 percent tariffs on Mexico if it did not do more to curb migration and the flow of drugs.

“But there aren’t clear mechanisms for the Trump administration on how to engage in dialogue and negotiate. That will resolve soon enough” once he assumes office, Mr. Olson added.

The incoming U.S. administration will likely try to get Latin American countries to agree to accept asylum seekers from other nations that are seeking refuge in the U.S., known as “safe third country agreements.” The first Trump administration was able to get Guatemala, Honduras and El Salvador to sign those pacts, though the policy was only implemented in Guatemala, albeit fleetingly.

But those agreements may be trickier to forge this time. President Bernardo Arévalo of Guatemala told The Associated Press this week, “We are not a safe third country, nobody has proposed it.”

His foreign minister, Carlos Ramírez Martínez, said in an interview that he expected his government would face pressure. “I don’t doubt that that’s coming,” he said.

Officials in El Salvador have said that they will work with the Trump administration to protect the status of Salvadorans in the United States. “We are working so that migration can be an option not an obligation,” Cindy Portal, a senior foreign ministry official, said in a television interview on Wednesday.

Absent clarity from the transition team, some Latin American leaders are instead crafting a united response in anticipation of any executive orders related to immigration or deportations issued once Mr. Trump takes office.

Representatives from several regional governments gathered in Mexico City this week to discuss the “opportunities and challenges of migration in the region and the strengthening of coordination and cooperation,” according to a Guatemalan government statement on the meeting.

The agenda, although heavy on migration, did not mention Mr. Trump.

Jody García contributed reporting from Guatemala City; Joan Suazo from Tegucigalpa, Honduras; and Gabriel Labrador from San Salvador, El Salvador. James Wagner, Paulina Villegas, Emiliano Rodríguez Mega and Simon Romero contributed from Mexico City; Mary Triny Zea from Panama City; Julie Turkewitz from Bogotá, Colombia; Hogla Enecia Pérez from Santo Domingo, Dominican Republic; Ed Augustin from Havana, Cuba; and Lucía Cholakian Herrera from Buenos Aires, Argentina.