Actually having worked in Canada each week for several years now, the local Canadian politics involved with proposed pipelines is quite interesting.
The real driver in Canada for Keystone XL is that they hope the threat of building it will drive the building a pipeline to either the west or east coast of Canada (more on this later).
The problem in Canada is that all the provinces and Indian tribes (First Nations, etc.) are effectively independent entities and can demand large royalties & payments for allowing a pipeline across their land. Currently the royalty demands from all these individual entities to run a pipeline to the west coast of Canada would add $45 or more to each barrel of oil.
This drives KeyStone XL as a threat to these Canadian entities to make reasonable monetary demands or otherwise Canadian companies will build XL and just keep exporting oil to the U.S. This threat is also used to drive the potential building of refinery capacity at the Canadian coasts.
While the demand for oil in China is growing, it imports most of its oil from elsewhere. It is not likely to become a big importer from North America. A better market for Canadian oil is Europe, but building a pipeline to the east coast would require a very lengthy and expensive pipeline.