Canadian oil producers expect the discount on their crude to shrink significantly when the Trans Mountain pipeline expansion (TMX) starts this year, but the relief may be short-lived as surging supply looks set to exceed the country's pipeline capacity in just a few years. TMX will ship an extra 590,000 barrels per day (bpd) of crude, trebling existing capacity to Canada's Pacific Coast once the C$30.9 billion ($22.8 billion) expansion is finally complete. For much of the last decade, oil companies in the world's No. 4 producing country have been forced to sell their barrels a...