Canada could potentially use oil and gas exports as a lever in negotiations if U.S. tariffs on Canadian imports escalate, Foreign Minister Melanie Joly told a Toronto business audience on Wednesday. Canada is vowing to impose tariffs on C$155 billion worth of U.S. imports but has so far not suggested it would reduce exports of commodities to the United States. Canada exports about 4 million barrels per day of oil to the United States, approximately 90% of its total crude exports.