US President Donald Trump has said his tariffs on Canadian goods are necessary to force action on the migrants and drugs entering the United States through its northern border. He has also described billions of dollars in daily cross-border trade as a US subsidy and claimed Canada would not be "viable as a country" without it.

U.S. tariffs that took effect on Tuesday are threatening to derail Canada's fledgling economic recovery and will fuel a rise in consumer prices and unemployment, potentially triggering a recession.

Trump said he was granting exemptions to tariffs on goods that come under a previous trade pact until 2 April.