Last week, Prime Minister Mark Carney admitted he had prepared for the once unthinkable scenario of a US invasion.
Noting that the risk is low and the likelihood is extremely low, he told the New York Times that he must consider all possibilities as relations between the United States and Canada are redefined under Donald Trump's presidency.
“It’s just risk management,” Carney said.
Having seen enough of Trump's global tariffs and his frequent statements about his desire to make Canada the 51st state, Canada decided to conduct military exercises simulating an attack from the Americans.
In 2025, the US President said it was "extremely unlikely" that the US would ever use force against Canada. Instead, he said, he would continue to apply economic pressure to achieve political goals.
"President Trump has done more than anyone to protect the great people of Canada," the White House said in a statement to the BBC.
Military experts spoken to by the BBC also consider an invasion unlikely, pointing to the numerous forms of defense cooperation between the two countries.
However, this issue clearly haunts Canadians.
In January, following the US military's capture of Venezuelan President Nicolas Maduro, a Leger poll found that more than 30% of Canadians believed a US invasion was likely.
Why is this unlikely?
A war between Canada and the United States would be complex and virtually unimaginable, said Lt. Gen. Christopher Coates, a former Royal Canadian Air Force officer with 34 years of service who served in various leadership positions.
"I have been involved in military operations throughout my career and we have never considered the possibility of a military attack from US soil," he told the BBC.
Coates, who has participated in NATO missions, noted that Canada and the United States cooperate in many aspects of military defense.
Both countries are members of the North Atlantic Defense Alliance, which obliges members to defend another member country if it is attacked.
In addition, both countries conduct joint Arctic defense missions under the North American Aerospace Defense Command (NORAD) and frequently share intelligence information.
In this regard, Coates stated that he believed that a US attack on Canada would not begin with an armed invasion, but rather through more subtle means such as cyber warfare.
Not always best friends
In the second half of the 20th century, after World War II, Canada and the United States became natural allies and achieved a high degree of integration in the economic, military and cultural spheres.
But it wasn't always like this. According to Tim Foran, a researcher at the Canadian War Museum, one of the core principles of Canadian identity is resistance to US expansionism in the 18th and 19th centuries.
“Fear of the United States is at the core of the political project called Canada,” he said.
Canada formed as a union of British North American colonies that remained loyal to the British crown when the colonies in what is now the United States rebelled.
Before the formation of Canada, the United States attempted to invade Britain's North American colonies: in 1775, it captured Montreal and nearly conquered the city of Quebec.
During the War of 1812, Americans repeatedly invaded what was then known as Upper Canada, Lower Canada, and the Maritime Colonies, leading to a stalemate. During that war, British troops burned down the White House in retaliation.
Foran noted that at that time, the colonies that later became Canada relied on Great Britain and its Royal Navy for defense, as well as the indigenous peoples who served as generals in major battles.
After World War I, Canada again considered war with the United States in response to its growing power and influence.
A plan was developed based on the results of secret trips by Canadian army generals to border towns, where they posed as tourists and photographed bridges and highways for reconnaissance purposes.
They also talked to local residents to better understand the possible enemy.
According to Andrew Burtch, a researcher at the Canadian War Museum who specializes in 20th-century Canadian history, war was an unlikely scenario at the time, but Canadians preferred to be prepared for it.
“It’s part of the military’s job,” he said. “They are thinking through all sorts of different scenarios.”
What a US invasion might look like
Matthew Schmidt, an assistant professor of national security at the University of New Haven in Connecticut, said that while a U.S. invasion is extremely unlikely, the very fact that Canadians were training shows how radically the world order has changed.
He added that Canadian leaders are really going to have to ask themselves tough questions about how closely they want to continue to work with the U.S. military — a partnership that gives the U.S. valuable information in case it wants to harm Canada in any way.
“It does damage the relationship with the United States, and there are some legitimate concerns,” he said.
Americans may not take Trump's talk of making Canada the 51st state seriously, he said, but Canadians clearly take them seriously - and are prepared to defend themselves if necessary.
So what could the scenario be?
The first phase of the war may be quite short.
According to the model used by the Canadian Armed Forces, reported by the Globe and Mail earlier this year, if attacked by the United States, Canada's strategic positions would be overrun within a week.
The Canadian Armed Forces would quickly find themselves outnumbered, forcing them to resort to guerrilla warfare.
Canada would ask allied countries such as France and Britain for support and protection, the newspaper reported in January, citing senior government officials.
The theoretical model is believed to be the first time in a century that Canada has developed a contingency plan in the event of an American attack.
According to Lt. Gen. Christopher Coats, the model is a less serious part of military planning.
He noted that Canada, unlike its NATO allies, had lagged behind in having a response plan in case of any ground invasion and was now trying to catch up in an era of unpredictable geopolitics.
According to him, this is, in particular, evidenced by the recent call by the head of the Canadian Ministry of Defense for a radical increase in the size of the armed forces, including by recruiting up to 300,000 poorly trained soldiers from among the country's citizens.
Schmidt stressed that Canadian and American soldiers regularly conduct joint exercises and treat each other with respect.
However, in the unlikely scenario in which relations deteriorated to the point of armed conflict, the United States, according to Schmidt, would likely focus on seizing valuable Canadian resources such as oil and minerals, as well as seeking to decapitate the country's leadership.
“You would be witnessing an operation that would perhaps be reminiscent of what happened in Venezuela,” he said, referring to the U.S. military operation earlier this year to capture former Venezuelan President Maduro.
While he acknowledged that the United States has great military capabilities, he noted that "given a level playing field" Canadian troops would have been able to fight back.
