Would it be cheaper and less problems if they just built a new refinery at the site of the oil?
And then build new pipelines for gasoline, diesel, and other products?
The market is not at the location of the source of the oil.
You'd still have to transport the refined products, and you'd be duplicating existing refinery capacity. A pipeline seems to me to be the cheaper and more straightforward solution to the delivery problem.
Also, from the US point of view, the supply of crude to the US would be well defined--it would be a long-term, reliable arrangement.
Then you would need a "products pipeline" to get the output to market, rather than a "crude oil pipeline" to get it to a refinery.
The market for refined products in Northern Alberta is, shall we say, rather thin.
If there was a better economic answer than the Keystone XL pipeline, one can assume the principals would have proposed it.
There are, in fact, several hundred thousand miles of pipeline buried under U.S. soil already.