According to people familiar with the situation, no clear-cut solutions have emerged - with the most promising option appearing to be importing via rail, as well as increasing pressure on existing lines or installing larger pipelines along permitted routes.

That said, those options would provide limited relief because rail transport is expensive, and existing pipelines are at or near capacity. One such pipeline, Enbridge's Mainline system, carries 2.85 million barrels of Canadian crude daily from Alberta to the Midwest - however company officials say it's running at full capacity.

Canadian officials say expanding the Keystone XL pipeline network is the way to go - and would offer a larger, more efficient solution. The project would have carried 830,000 barrels a day of Canadian crude to Nebraska, and then on to refineries on the US Gulf Coast.