Air Canada and Porter own the east, and WestJet attempted to be a leisure airline in a business market. What they failed to realize is the majority of people are not flying from YUL of YOW to YYZ to then connect to sun destinations. They'll simply plan their vacation around the one or two YUL direct CUN flights a week. WestJet was making money hand over fist when they were doing the point-to-point leisure flying. So soon as they moved to the hub-and-spoke model, they started losing money. Profitable, yes, but decreasing YOY. The 787 was a mistake for the company to get into. They should take the ones they have and fly them to the popular sun destinations. Convert the other orders and options into 737s. As for the Q400, the only reason it exists is to support the 787. To convert that flying into the lower demand routes where a 737 point-to-point doesn't make money and leave the rest to the Boeing fleet. That's still a lot of flying out west that the Q4 will do, but the Eastern Triangle certainly didn't need yet another Dash operator doing yet again hourly flights.
There are only 37 million people in Canada, most of whom don't travel with the airlines on offer. Airlines have to find their niche and stick to it. Flair is great until the first time you want to get to Toronto on the cheap to connect to Dubai to find out that Flair cancels and now AC doesn't have to do a thing for you. Next time, you'll just take AC all the way. As for Porter. They're about to learn the hard way just as WestJet did. Unfortunately for them, they can't retreat back into the vacation market. They'll have to tough it out and hope AC decides to buy a few more Q400s and Embraers.
It blows that this is how aviation is in Canada. But, it's a big country with a small population trying to play to the same tune as America (big area, big population) and Europe (small-ish area, big population).