Obama is not America. He is not king. Arguably, he is not a legitimate president. So find a better argument.
The U.S. refuses to buy our product. That finally wakes us (Canadians) up to the dangers of dealing with a monopsony buyer. We look for other willing buyers, and discover there are plenty of them. We have the choice of selling to those willing buyers, or having our entire economy collapse. We do what any rational person would do (and that includes Americans, if put in the same situation) — and we make a sale.
I've gotten inured to leftist envirofascists trying to shut down oil-sands production — I'm more than a little astonished to see the same sort of arguments coming from longstanding members of this forum.