That's an interesting spot you're in Maddogrider. I suppose you have to ask yourself what is more important: the money or the passport?
The issue you'll face coming back to Canada and joining the airlines is, like everywhere, seniority. Although the OP started this thread over a year ago, not much has changed, and it is still a very relevant thread. You have your two choices: come back now and get your number, or wait and put yourself in a position to wait a very long time for the left seat again. Waiting two years from now would put you smack in the middle of where my financial advisor believes the next recession will be, so you might come back to find there are no jobs. Of course, people in finance are always saying that the sky will fall, and they only need to be right once to be considered a savant. Thus, you're back to the original question: what is more important to you?
Regardless of your answer, here is what I think is the most up-to-date view of the industry. Take it with a grain of salt though. Winter is coming, heck it's here in some spots, and once that snow falls for real across the country, it's anyone's guess at how the industry looks in spring.
Air Canada has hired a lot of younger pilots in the past few years, and from what I've been shown their peak retirement wave has or will crest in the next year or two. That's a whole lot more pilots younger and ahead of you, meaning that if you did go to AC, you might be waiting a very long time for the left seat again, if that's important to you. A few friends over at AC all agree that the next 15 year FO is about to arrive or already has arrived on property, and they don't mean the 15-year waiting to bypass reserve either. The good news here is even if they're past peak retirements, the wave lasts until something like 2032, so there is still time. Air Canada also has a lot of orders to be filled, which when combined with the retirements, may make those upgrades last a little longer. They're expected to take delivery of 35 aircraft next year, but those will be filled by those pilots on property and those hired next year (obviously). Once all those younger pilots upgrade onto the widebodies, things will come to a grinding halt for years, which is why my buddies to believe the next 15-year FO is already there.
WestJet don't have as many retirements, but the ones they do have peak in two to three years. Their retirement window is also much shorter, something like 2026 to 2032 and within that window I seem to remember the highest projection was something like 300 in one year. Back in full swing WestJet was hiring that in one year, so retirements won't make as much of an impact as they did at AC. WestJet is not hiring right now, but the rumour is that they will be from next year and, again, that's a lot of younger pilots ahead of you. WestJet is also famous for their 10 to 12 year upgrades which, even with their Max-10 and 787 order won't do too much to stop long upgrades once they're all on property, the first Max-10 is supposed to arrive Q3 or Q4 next year and the next 787 by 2029 or 2030, but that assumes the FAA doesn't have more to say regarding certification of the Max-10. There is also some talk that with delivery of the Max-10s, the fleet will shrink as the -700s and early -800s are returned, potentially negating the impact the retirements will have, and making the situation for future upgrades even worse.
Porter is your other serious option. They don't have any future orders that I'm aware of and at this point have maybe one or two more E195s to take delivery of, so internal growth will stagnate. They also seem to be a younger pilot group - much like WestJet was back in the early 2000s, so movement will rely on attrition. They're being very aggressive right now to find the profitable routes, and make a foothold, which is why they're always in the news. They're making good progress, and have an amazing onboard product, but they're helped along by having warranties on those bright white jets. Once those warranties disappear, their CASM will increase and it remains to be seen whether their product will suffer as a result. They have enough experience though to know how to counter that CASM increase, but they're also prime targets for some investment firm to come in and skin them to bone, just like Onex did with WestJet. I hope I'm wrong on this one, I really want to see Porter stay with the Dulce family. I'd like to think Michael Deluce will stick around for as long as his old man has, but money does a lot of talking, and they've tried to sell Porter before - famously to WestJet before Encore was started - so I believe it's just a dollar amount they're waiting for.
Your other options for major airlines are Flair, Canadian North, and Air North. It's anyone's guess as to where Flair will be in two months, nevermind two years, and Canadian North just issued a layoff notice earlier this month. I don't see them going anywhere, but they won't be hiring any time soon. Air North fills an important niche market, and those pilots accept upgrades as long as WestJet for the lifestyle they live, so those jobs are hard to come by.