President-elect Donald Trump's threatened tariffs could prompt Canada to pursue dollar-to-dollar retaliation or an export tax on oil and gas bound for the U.S.

Trump's biggest first-term trade impact was to shatter decades of political consensus favoring ever-lower trade barriers.

Should President-elect Donald Trump follow through on his promise to impose a new 25% tariff on goods imported from Canada, the United States' northern neighbor has vowed to retaliate in a trade war that could prove costly for American consumers.