Certainly in the short run. Canada need the pipeline to the Gulf Coast to ease what soon will be a glut of Bitumen in Alberta as Oil Sands production continues to ramp up.
If Keystone XL isn't built, refineries on the Gulf Coast will still get oil from off-shore, either Venezuela, the Middle East, or Africa. Whether it will be as secure a long-term supply is questionable, but short term the United States can find oil for its refineries elsewhere.
Keystone XL is not a done deal but it is still the nearest option for expanded Canadian oil shipments. If it is approved this year it could be operational in 2015.
Northern Gateway looks less likely and even expansion of the Trans-Mountain still needs approval and will take longer to build.
Canada needs Keystone XL, and it needs it more than the U.S.