The keenest observer of the all-out trade war between the United States and Canada is surely President Xi Jinping of China. If Washington doesn’t change course, he’s probably going to be its winner, too. 最热切的美加全面贸易战观察者莫过于中国国家主席习近平。如果华盛顿不改变方向，他很可能也将成为这场冲突的赢家。…