"It is clear that there is broad consensus across the provinces that we need to continue to keep our current border measures in place," Trudeau said after consulting with provincial leaders.

"We will keep discussing with the United States administration on ways forward," he told a daily briefing. "Our priority on this is to ensure that we're keeping Canadians safe while continuing to ensure the flow of essential goods and services."

The world's longest international frontier -- at 8,900 kilometers -- was closed to all non-essential travellers on both sides on March 21 in response to the coronavirus crisis.

The border was originally set to reopen in April but the closure was twice extended, until at least June 21.

The closure has led to a massive drop in cross-border traffic -- of up to 95 percent, according to Statistics Canada -- but trade has continued unabated.

Prior to the pandemic, Can$2.4 billion (US$1.7 billion) worth of goods and more than 400,000 people crossed the border each day on average.

Ottawa last week announced an exemption to allow thousands of foreign nationals to reunite with their families in Canada, following reports of hardship cases such as an American looking to join his Canadian wife for the birth of their first child.

They must, however, self-quarantine for two weeks upon arrival. 

A loophole allowing Americans from southern 48 states to transit through Canada to Alaska, meanwhile, has raised fresh concerns.

Several travellers were reportedly observed recently flouting rules requiring them to take a direct route, and to social distance at stops along the way.

Banff residents, for example, told public broadcaster CBC they'd spotted license plates from Texas, Washington and even New York, and overheard tourists joking about how easy it was to get to the national park.

Trudeau said his government was "looking into" the reports, adding: "We need to make sure that we're able to apply the rules consistently."