The plan to develop closer international ties in key sectors was laid out in a report from the Public Policy Forum, a non-profit group that brings together experts to advise on significant policy issues.

The ambassadors said the relationship between Canada and the U.S. benefits from mutual commercial and security interests and "is one of the world's great win-wins."

"Our intimate ties atop North America and into the wider world also require constant tending," the letter said. "This is particularly true now, amid rapid and complex geopolitical change."

The signatories, who represented Canada in Washington for more than 20 years dating back to 1989, include Derek Burney, who was ambassador under former prime minister Brian Mulroney and later the head of prime minister Stephen Harper's transition team, and John de Chastelain, also appointed under Mulroney and was the former chief of the defence staff for the Canadian Armed Forces.

Raymond Chretien and Michael Kergin, who were appointed under prime minister Jean Chretien, also signed the letter as did David MacNaughton, who served as ambassador from 2016 to 2019 during the challenging years Canada was renegotiating the North American Free Trade Agreement with the Trump administration.

The renegotiated deal, known as the Canada-U.S.-Mexico Agreement, will be reviewed in 2026. That means whoever wins the November election will be at America's helm for the critical review, and both presidential candidates are selling protectionist policies that could cause uncertainty for Canadian trade.

Vice-president Kamala Harris was one of 10 U.S. senators to vote against the trilateral agreement under Donald Trump, saying it didn't do enough to protect American workers or the environment.

Meanwhile, the former president has campaigned on plans to increase tariffs on imports and threatened that he would not defend NATO members who don't meet the alliance's defence spending targets, of which Canada is one.

Prime Minister Justin Trudeau promised in July to meet the target of spending two per cent of gross domestic product on defence by 2032.

While Canadian officials have been connecting with Democrats and Republicans about bilateral interests across the U.S. for months, some business groups and experts have said more needs to be done to ensure Canada is prepared for an increasingly unstable neighbour no matter the election outcome.

The report, released by the Public Policy Forum and the Munk School of Global Affairs at the University of Toronto on Wednesday, said Ottawa has a chance to play to Canada's strengths and align its national interests with those of its close partners, especially the U.S.

It suggested Canada focus on four high-impact sectors: Arctic security, critical minerals, energy and the environment and technologies like artificial intelligence and quantum computing.

The report said those sectors should be "continentalized," requiring production and investment across both sides of the international border, to deepen and broaden the relationship between Canada and the U.S.

Canada and the U.S. are integral to one another's economic and physical security, the ambassadors wrote in the letter.

The ambassadors noted their signatures "should in no way be interpreted as criticism of any of the governments we faithfully served" but as a recognition that circumstances in the world have changed and Canada needs to seize opportunities

"Canada needs a renewed strategy," they said.

This report by The Canadian Press was first published Sept. 18, 2024.