Trump’s new Canadian tariffs arrived after eleventh-hour trade negotiations disintegrated. Canada promises matching retaliation after automotive tariffs helped sink a possible deal. Carmakers face more uncertainty as North America’s key trade relationship deteriorates. Just when it looked like America and Canada might be ready to put their tariff boxing gloves away, somebody rang the bell for another round. The US has imposed 50 percent tariffs on around $20 billion worth of Canadian goods after eleventh-hour negotiations between the neighbors spectacularly fell apart, and Canada says it will apply the same levies back. The new duties on Canadian goods cover a random shopping list stretching from hockey equipment to dairy products, alcohol and flower bulbs. More importantly for the auto industry , the breakdown reportedly came partly because Washington and Ottawa couldn’t agree on how Canadian-built vehicles should be treated. Related: W...