Donald Trump's been president for a week, but in those seven days he's already signed a dozen or so executive orders and memorandums that will fundamentally change relations with his nearest neighbours for years to come.

With a single stroke of his pen Wednesday Trump began reshaping U.S. immigration policy, kick-starting his plans to build a wall on the border with Mexico while cutting off federal funding to cities — including some close to the Canadian border — that have been refusing to detain undocumented immigrants.

The target, of course, is Mexico.

But Stephanie Carvin, a former national security analyst with the Canadian government who now teaches at Carleton University, says those decisions represent a serious challenge for Prime Minister Justin Trudeau.

"We are going to have to reassure the Americans that our vetting process for immigrants and refugees is consistent with their own so that there's no issue about security," Carvin said.

Motorists in line at the U.S.-Mexico border on January 25, 2017 in Tijuana, Mexico. (Sandy Huffaker/Getty Images)

Canada lifted its visa requirement for Mexican travellers in 2016, but said the decision would be revisited if refugee claims rose to 3,500 a year. Carvin says it's not unreasonable to expect that threshold will be reached this year with the changes Trump's initiated.

At a stop in Winnipeg Thursday, the prime minister was asked for his take on the U.S./Mexico situation, and how Canada would respond if there's an increase in refugee claimants.

He will find an excuse to turn on Canada. - Agustin Barrios Gomez, Mexican Council on Foreign Relations

"Canada has its policy on refugees and immigration," he said. "We set out the approach, which is open and rigorous and making sure processes are followed and security is strongly addressed and respected."

Agustin Barrios Gomez, a former Mexican congressman and founder of the Mexican Council on Foreign Relations think-tank, says Trudeau has to stand up to Trump.

"The only documented case of a terrorist trying to enter the U.S. via a land border was on the Canadian side, not the Mexican side, so it's just a matter of time — he will find an excuse to turn on Canada," Gomez said in an interview this week with Rosemary Barton on CBC's Power & Politics.

'Pressure to bend' on torture

Trump's pen isn't the only source of concern in Canada. So are his words.

In an interview Wednesday with ABC News, the president insisted torture works as a way of getting information vital to American security. His comments are raising the spectre that the abandoned and discredited "enhanced interrogation techniques" first introduced by the George W. Bush administration after the 9/11 attacks could be brought back.

"I have spoken as recently as 24 hours ago with people at the highest level of intelligence and I asked them the question, 'Does torture work?' Trump said. "And the answer was, 'Yes, absolutely.'"

A return to practices such as "waterboarding" would require Canada to reconsider how it shares information with the United States and other members of the so-called Five Eyes network, says University of Ottawa law professor Craig Forcese, who's written extensively on this country's own anti-terrorism laws.

"The concern is whether Canada can remain in a close, seamless relationship of information-sharing with a Five Eyes partner that is not complying with international law," he says.

It's a concern for the U.K., as well — another member of Five Eyes. On Thursday, the Guardian newspaper quoted a former British diplomat who said that country's security agencies would be torn between a moral and legal obligation not to be involved with torture, and their heavy dependence on the U.S. for intelligence.

Forcese said similar concerns exist in Canada.

"Our agencies are net importers of intelligence from the U.S. They would have to screen everything that's coming in," he said. Forcese is worried agencies such as CSIS and the Canada Border Services Agency "would feel pressure to bend on the torture question rather than stop the flow of information."

Carvin agrees. She says there's no appetite for a repeat in Canada of what happened to Maher Arar, the Canadian who was deported from the U.S. and tortured in Syria after Canadian officials shared information without proper safeguards.

"And there's a consensus that it [torture] doesn't work because there's no way to ensure the information is even accurate," Carvin said.

U.S. steel and trade deals

Trump also moved quickly this week to withdraw the U.S. from the Trans-Pacific Partnership trade deal, and to clear the way for the Keystone XL pipeline — provided it's built with American steel.

Warren Everson, senior vice-president of the Canadian Chamber of Commerce, says Trump's executive orders may not be aimed at Canada, but this country is going to feel the impact.

Opponents of the Keystone XL and Dakota Access pipelines held a rally at Lafayette Park, next to the White House, the same day Trump signed executive orders advancing their construction. (Saul Loeb/AFP/Getty Images)

"It should raise warning flags in Ottawa and among premiers. We are not very efficient. We are not very competitive. And our governments need to get concerned about it," he says.

"They have to be mindful that a carbon tax, enhancements to the Canada Pension Plan and increased regulations increase the cost of doing business at a time when the U.S. is putting a new emphasis on attracting jobs and investment."

Laura Dawson takes a different view.

The director of the Canadian Institute at the Wilson Center in Washington, D.C., says Trump's only concern is preventing China from dumping cheap steel into North America.

For example, she says the proposed Gordie Howe International Bridge between Windsor, Ont., and Detroit — which is on Trump's priority list of 50 national security projects, includes a provision that it be built with "North American" steel.

The list also includes reconstruction of the Soo Locks that link Canada with Michigan and the Peace Bridge between Buffalo, N.Y., and Fort Erie, Ont.

"Canada will get some positive spin-off from that because the steel industry here is so heavily integrated," Dawson said.

Confusion. Trepidation. Both signs that Trump represents a departure from the normal balance in Canada-U.S. relations.

And we're only one week in. A dozen executive orders are already out, with more to come as Trump puts his America First policies into effect.