President Donald Trump's threats to impose punishing tariffs on Canada and Mexico may be part of a strategy to gain leverage ahead of new negotiations on a regional trade agreement, experts said.

The focus on American prosperity and national security is the latest pivot by Canadian officials as the country tries to find its footing with the new Trump administration, and - more urgently - avert the threat of blanket 25% import tariffs imposed by the US, its largest trade partner and closest ally.