Canada could use 2 key exports as leverage against Trump. One premier says that's a bad idea.

Canada is the world's largest exporter of potash, a key fertilizer ingredient. Heywood Yu/Bloomberg/Getty Images Canada is hitting back at the US with billions of dollars in tariffs on US goods. Saskatchewan's premier says using oil and potash as leverage would hurt Canada, too. The trade fight is escalating, with Canada retaliating and President Donald Trump threatening even more tariffs. Canada is escalating its response to President Donald Trump's trade war, with another round of…