The left - Liberals included have been stalling this project for years. So the Liberals did have something to do with it. 
I have stated in the past I would have killed Keystone for Energy East. We need the capacity to export to the wider world and benefit from world prices , not discounts to the Americans. 
As for low oil prices I believe they were at one point $10 in the 1990s. They ran up in excess of $100 in 2014. Oil demand still grows and the fracking technology requires low interest rates to fund production. Interest rates are rising.
Best cure for low prices is low prices.