Canada’s tariffs on about $20 billion in U.S. goods have taken effect, responding to President Trump’s latest tariffs. Here’s what to know. ↧ What to know about Canada’s escalating trade war with the US as C... Canada’s retaliatory tariffs on about $20 billion worth of U.S. goods take effect Tuesday, turning its escalating trade war with President Donald Trump into a test watched far beyond the border: Can a country much smaller than the United States stand up to Trump and succeed?