I dislike disagreeing with my friends in the environmental movement, but I am going to come down for letting the Canadians build their XL pipeline in the US. This is an issue where both sides have way overhyped the issue, with neither the environmental damages nor the supposed economic boost in teh US as bad or gas ood as either the critics or the supporters claim. It is a mostly pretty small stuff, but huge noises and huffing and puffing have gone down on both sides, with it becoming highly partisan, just to totally distort things. I would link to Jim Hamilton now, but his posts on this were ages ago, but this was his bottom line: this is a normal garden variety deal like what goes on in the US all the time (see fracking for oil and gas in North Dakota), turned into a big deal because it is a cross-border deal.
Cutting to the most recent chase is the freshly-delivered State Department report that says it essentially has no impact on global warming. Why is that? Because even if Obama kills it, the Canadians will still develop their tar sands and sell the output to China, probably sending the stuff across the Rockies to Vancouver to ship, either by train or pipeline, which will almost certainly entail a higher risk of ground environmental damage due to spills, plus damage to global warming due to or say "blame Canada," but they are currently the best friend of the US, despite a long history of the US ignoring their interests and violating trade and other treaties, with the US having a long history of sending pollution of various sorts, including acid rain, across our mutual border into Canada, damaging their forests and fisheries, which they are far more dependent on economically than we are in the US.
We have had a long history of ignoring them on such matters, and even though now our environmentalists might say that we are on the side of virtue for once, sort of, I do not see the damage to our relations with them worth the, frankly, zero gain to the environment that will occur by slapping them in the face on this matter. Just say yes and build the damned thing. Those tar sands are going to get developed no matter what anyway.