Shorting is extremely hard to get right. There are simply too many ways you can be right and still lose money.

Canadian oil producers like SU, CVE, CNR are all pretty well capitalized. They are run a lot more conservatively than the American shale companies. These companies won't be profitable with oil at $20, but they won't be going bankrupt anytime soon either. With near term bankruptcy out the window, shorting these companies is basically shorting a long term call option on oil prices.

This is a very bad idea, because oil has very limited room to fall and a ton of room to rise. There are just too many unforseeable events that can drive oil prices. What if a war between Iran and the US starts? What if there is an armed coup in Saudi Arabia? Low oil prices tend to drive social instability in oil exporting countries. All sorts of things can happen that would cripple production and export capacity.