Six Lego-like concrete blocks mark the end of a rural road at the U.S.-Canada border. The police vehicle, revving through blowing snow, crunches to a stop.

The barriers, installed last August in a joint venture with President Joe Biden's administration, stop vehicles bearing migrants from barreling across the border into the United States.

But they do not stop migrants crossing on foot.

"People can still hop over them," said Royal Canadian Mounted Police (RCMP) Sergeant Daniel Dubois.

Canadian police say they have installed more cameras and sensors over this section of the border over the last four years. Ottawa promised this month to deploy more officers and technology targeting southbound border-crossers after U.S. President-elect Donald Trump threatened Canada and Mexico with sweeping 25% tariffs if they do not reduce the movement of migrants and drugs into the U.S.

But Canadian law enforcement officials acknowledge they are limited in what they can do to stop southbound migrants.

"Even if we were everywhere, we couldn't stop it," said Charles Poirier, an RCMP spokesperson in Quebec.

Canadian authorities turned back about 1,000 people trying to cross into Canada between formal crossings in the 12 months ending in October, according to data obtained by Reuters, compared to more than 23,000 apprehended on the U.S. side by U.S. Customs and Border Patrol. The apprehensions of U.S.-bound migrants doubled from the previous year but still represent a tiny fraction of the 1.5 million apprehensions over the same period near the U.S.- Mexico border, which experiences higher irregular migration overall.

At the Canada-U.S. border, recent movement has been southbound. That could change.

Canadian politicians admit the show of strength at the border is in part about creating an impression of security.

"We have a very important activity to undertake to make sure that we give confidence to the U.S. that we have an immigration system that they can manage for," Canada's Immigration Minister Marc Miller told a private meeting last month with the Canadian Council for Refugees advocacy group, according to a recording obtained by Reuters.

Miller was not available for an interview.

PATROLLING THE WORLD'S LONGEST LAND BORDER

Reuters spent four hours with RCMP officers patrolling part of a 105-mile (170 km) stretch of the border known for frequent migrant crossings, watching out for tips from the public; calls from U.S. authorities; suspicious movement captured by surveillance cameras and erratic drivers suspected of carrying potential crossers.

Securing the world's longest land border - about 4,000 miles (6,400 km) across forests, fields, ditches and lakes - is a gargantuan task. And police cannot arrest migrants who are in Canada legally, even if they suspect they intend to cross, Poirier said.

Four migration experts Reuters spoke with were unsure what the promised new border security technology and equipment would do to prevent crossings.

Refugee advocates argue that the restrictions do not deter migrants but put them at greater risk. At least nine people have been found dead near the Quebec-New York border since a 2023 rule change allowed each country to turn back asylum-seekers crossing between ports of entry.

"The only thing that you do is that you are pushing people to risk it," said Action Refugies executive director Carlos Rojas Salazar.

Some migration specialists suggest preventing potential U.S.-bound migrants from entering Canada in the first place could be a more effective strategy.

Police told Reuters they have stopped people at the border coming directly from the airport but could not say how many.

Canada earlier this year started refusing more visas and turning away visa-holders at ports of entry.

CITIZEN SURVEILLANCE

Terry Rowe, a resident of Champlain, New York, whose home lies about a mile from the Canadian border, set up six motion-sensing cameras on his property to watch the wildlife. He ended up watching migrants.

He pulls out his phone to play an eight-second night-vision clip of a figure carrying a backpack and trundling across the snow.

He figures he has amassed more than 40 such videos over the past three years.

"It makes us a little nervous - you know, when it’s 70 feet from your bedroom window," Rowe said. "We keep our doors locked. We have our cameras. We have our wild, vicious animals here."

He regularly reports people crossing through his yard to U.S. border patrol, he told Reuters. For southbound crossers, they usually show up within minutes. "Going north not so much," Rowe said.

Rowe said U.S. authorities used to offer rewards for apprehensions. Canadian police said they encourage residents to report migrant crossings.

Until last month, most of the traffic was from Canada to the U.S., Rowe said.

That may be about to change. Canadian law enforcement is bracing for a potential influx of migrants fleeing Trump's threat to carry out mass deportations once he is in the White House, Poirier said.

"We've redeployed some officers right here at the border to make sure that if there is a surge in migration, we'll be ready for it," he said.

From Rowe's vantage point, it looks like that surge might already be starting.

Of the most recent five people he has seen crossing, four have been northbound, he said.

(Production: Carlos Osorio and Arlene Eiras)