I'd like to skip over the land-rights issues for a moment and address a couple of environmental related issues.
Cancelling the Keystone Pipeline is not a win for the environment. Without the Keystone Pipeline, that oil will move west to the Pacific coast along the soon-to-be-expanded Trans Mountain Pipeline, then by tanker to China where it will be refined.
I'm far from an expert on catalytic cracking, but by every account I've read, environmental regulations for refiners in America render American refineries much, much environmentally cleaner than Chinese refineries. In addition, we must also now account for the increased risk to international fisheries that comes from shipping a million+ barrels of oil per day across the Pacific.
I'm neither for nor against the cancellation of the Keystone XL pipeline, and I suspect I don't understand the tradeoffs well enough to have an informed opinion.... but when we are accounting for the tradeoffs, let's not forget the two I've outlined above.