If President Trump's tariffs against Canada take effect, Canadian Prime Minister Justin Trudeau said the U.S. would immediately face a raft of countermeasures on Tuesday. Why it matters: Trump's comments Monday that he would impose 25% tariffs on Canada and Mexico sent markets sliding amid fears it could start a trade war,

Canadian Prime Minister Justin Trudeau said he wouldn’t allow President Trump’s tariff decision to “go unanswered,” and set in motion the imposition of retaliatory tariffs targeting about $100 billion of U.