Canadian Prime Minister Mark Carney said emphatically Tuesday that Canada is "not for sale" and "won't be for sale, ever" in an Oval Office meeting with President Trump, moments after Mr. Trump called the border between the U.S. and Canada "artificial" and romanticized the idea of Canada joining the U.S.

President Donald Trump and Canadian Prime Minister Mark Carney met in the Oval Office on Tuesday, where they maintained a civil tone despite stark and unresolved differences amid an ongoing trade dispute that has strained decades of U.