Ottawa is ready to retaliate if U.S. president-elect Donald Trump slaps Canada with devastating tariffs, Prime Minister Justin Trudeau promised Friday — and his ministers say Republicans in Washington don't fully understand the likely impact of the duties on both countries' economies.

The government is preparing for the possibility that the incoming U.S. administration will impose high tariffs on Canadian goods, setting the close allies up for a showdown.

Canada could impose countermeasures on up to C$150 billion worth of U.S. imports if President-elect Donald Trump puts tariffs on Canadian goods and services, a source familiar with the matter said on Wednesday.