Canadian Politics Today

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It could be the fact that we have so few viable national parties.
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In Canada, we usually end up with 3 national parties with a significant presence in parliament, and 2 parties seem to dominate. It makes it trickier to put together a coalition, since you have fewer possible alliances

That’s due to FPTP.

Yes, that's probably a major part of it, with newer, smaller parties having a more difficult time obtaining seats. (Although I am sure history has something to do with it too...)

With a system that better represents the electorate, despite getting more popular vote, the parties on the left side of the spectrum would likely rule as a coalition.

Actually I would say its hard to predict what would happen if we used a different voting system. Its possible that instead of the current "Big conservative/Liberal, medium NDP, smaller green/Bloc/PPC, you might see other newer parties appear all over the political spectrum, or parties may start shifting their policies. (Maybe if we had a different voting system a few decades ago, we'd still have the Progressive Conservative party around.)

You might see Liberal/NDP coalitions, you might also see Conservative/PPC coalitions (not that I would want that). You might also see Liberal/Conservative coalitions, if we ever got to the point where neither the conservatives nor the Liberals would ever be able to form a majority, but they were concerned about extremism from both ends of the political spectrum.