I quite like the CR9s, they're not spacious, but no one's are. If the 12A seat still exists, pay for it. For a long time it was the best Econ seat in the fleet, a solo seat in economy, beautiful.
Beyond that it's just tight, but what other options do you have? PHX-YVR isn't a long flight, so unless you're really big or need extra legroom due to leg issues or something there's not really any reason NOT to opt for this flight. AC is also currently flying ORD-YVR on CR9s, I can't say I've ever flown one THAT far, but I did have one booked and was excited to see how it holds up.
I will offer this, I'd much rather fly AC CRJ than United, now I don't get free E+ seats, so that hurts the experience for me. But AC CR9s have AVOD in the seats, and I covet that. Even if I've seen everything, I always prefer watching at the built in angle rather than trying to prop up my iPad and crane my neck downward etc. I've taken a few flights that are conducive to hanging your iPad via the smart cover and some seats that have built in plastic holders that can be opened and close to fit the size of the device. But my personal preference is always built in AVOD. So while I'm not judging this based on the value of the points being used or anything, since often US-CAN flights are very cheap, I wouldn't hesitate to take this flight.