Canada is bracing for a surge of migrants to its southern border after Donald Trump doubled down on his pledge to conduct the largest mass deportation in American history.

On Thursday, Trump told NBC News there was “no choice” but to proceed in removing some of the estimated 11 million undocumented people in the United States.

During Trump’s first term in office, tens of thousands of Haitians fled to Canada after he ended temporary protected status for the group (it was later restored). Many passed through the Roxham Road crossing, a rural country road that served as funnel for refugees attempting to safely traverse the world’s longest land border.

That crossing was closed in 2023 after Canada and the US amended the Safe Third Country Agreement, expanding it to cover the entire land border instead of only formal crossings.

The RCMP says it has plans to deal with a fresh increase in crossings that has been “several months” in the making. A spokesperson for the federal police said officers had the “tools and insight” to deal with another increase, including a scenario in which hundreds of people cross every day.

If those crossing claim asylum, the RCMP cannot send them back to the United States. Instead, their claims are entered into a system with an estimated backlog of 250,000 cases. The average processing time for a case is 44 months, a parliamentary committee heard on Thursday.

Experts fear that with formal crossings closed to migrants, desperate families will take increasingly dangerous routes across the 5,500-mile border. In many locations, the terrain and the weather can be deadly.

In January 2022, a family of four – including a baby – died after attempting to cross from Canada to the United States. Police said the group died from the intense cold and punishing winds, where temperatures had dipped to -35C (-31F).

Last year, the bodies of eight people, including two young children and their parents, were discovered on the banks of the St Lawrence river near the Mohawk community of Akwesasne, which spans Quebec, Ontario and New York state.

Both cases involved groups heading from Canada into the US, but migrants heading north face the same challenges, which as winter approaches include sub-zero temperatures, deep snow and frostbite.

In Quebec, the province that absorbed most of the crossing, politicians warned the federal government was unprepared for a repeat of the last Trump administration.

Yves-François Blanchet, leader of the separatist Bloc Québécois party, said Ottawa was “refusing to acknowledge an obvious and very serious situation” and that more resources were needed to anticipate new routes used by human smugglers.

Quebec’s premier, François Legault, told reporters he did not believe the province had the capacity to absorb a significant number of new arrivals, adding that although border security falls under the purview of the federal government, his government would possibly send its own officers to monitor crossings.

Earlier this week, the deputy prime minister, Chrystia Freeland, said her government “absolutely recognize[d] the importance to border security and of controlling our own border, of controlling who comes into Canada and who doesn’t”.