Because, after all, it's not like American corperate interests, backed by their government, have screwed us over. And we all know about their excellent environmental record and their well documented concern for economic interests of their allies...
You'd think little things like getting shafted by their corperate & government interests (which seem to overlap rather heavily) on a regular basis would tend to make politicians a little more dubious regarding things like this.
Go here, and use the form at the bottom to tell they should blood well keep it in Canada, rather than giving the US yet another hold on our economy.
http://www.enorthernbc.com/Terasen-Petit