The Financial Post reports in its Tuesday edition that a report by National Bank citing C.D. Howe Institute research shows that Canada's interprovincial trade barriers are equivalent to a huge 21-per-cent tariff. Post columnist Martin Pelletier writes that it is shocking to think that it is more punitive to trade amongst ourselves than with the United States. Externally, Canada is facing one of its most serious threats in decades, with President Donald Trump having threatened hefty tariffs on our exports and whose full agenda will play out in coming months. In terms of energy plays, Mr. Pelletier thinks that any widening of the Canadian heavy oil differential and corresponding sell-off among oil producers would create an excellent buying opportunity, as he believes any tariffs on exports would be short-lived. He expects the Trump administration to want more Canadian crude rather than less, so any talk of pipeline expansions to tidewater -- especially Energy East -- would certainly help our cause. Other areas could be exposed, such as manufacturing, agriculture and lumber, but he wonders how pronounced any tariff would be. While this is a clear danger, perhaps it will lead to some much needed changes here at home.