Canada's former deputy prime minister Chrystia Freeland launched her campaign Sunday to replace Justin Trudeau as Liberal Party leader and prime minister, pitching herself as the best option to oppose incoming U.S. President Donald Trump.

Freeland had been one of Trudeau's closest allies in government since the Liberals swept into office in 2015, also serving four years as finance minister until her dramatic resignation last month.

In a scathing resignation letter, she accused Trudeau of putting his own political interest above the urgent need to prepare Canada for the potential threats of the incoming Trump administration, including a possible trade war.

Freeland's departure was seen as a devastating blow that pushed Trudeau to announce his plans to leave office.

Trudeau has said he will stay on as a caretaker prime minister until the Liberals choose a new leader, which is expected on March 9.

At an event officially launching her leadership bid, Freeland said "Donald Trump doesn't like me for one simple reason: I have been fierce, resolute and effective in defending Canada."

Trump, who retakes power on Monday, has threatened to impose a 25 percent tariff on all Canadian imports until Canada addresses what he calls the flow of undocumented migrants and the drug fentanyl into the United States.

Trump called Freeland "totally toxic" following her December resignation.

Freeland was a lead negotiator at talks to revise North American free trade agreements during Trump's first term.

Freeland on Sunday promised a "dollar for dollar retaliation" in response to any Trump tariffs.

"If you force our hand, we will inflict the biggest trade blow that the United States has ever endured," she said.

She blasted Trump's proposed tariffs as "illegal and unjustified."

In entering the race, Freeland immediately becomes a front-runner to replace Trudeau along with Mark Carney, who previously led the Bank of Canada and the Bank of England.

Carney has positioned himself as an outsider not tainted by the unpopular Trudeau.

The Liberals are trailing the Conservatives badly in polls.

That means the winner of the Liberal leadership contest may not serve as prime minister for long, as opposition parties have pledged to bring down the government after parliament returns on March 24, triggering a general election.