Well for my summer vacation this year, I'm planning to head out to Edmonton to visit my sister. I was checking flights from YFC and YQM on all 3 airlines, and I ultimately decided on Porter.
Prices were comparable, and the difference between YFC and YQM would have been eaten up by 2 weeks worth of parking at YQM and gas prices to drive down there (vs a taxi trip out and back to YFC).
I was first comparing AC vs Westjet, and did try to get Westjet to work, but the schedules just weren't nice for the days I was looking at (and the prices that were available.). I think I had looked at Porter briefly at first and dismissed it, but decided to go back and I'm glad I did (and even managed to snag a sale price). All in all, round trip prices to Edmonton and back in late July came out to around 700$ (after I did the checked bag and seat pick 'upgrades'). Oh and no Boeing planes either.
So yeah, from my very limited point of view, Porter is pretty firmly established as Canada's 3rd major airline and probably has a good chance of swapping positions with Westjet for second place the way things are going.