I collect with BA not with AA and I've just been advised on a separate thread here that I won't get either BA miles or tier points if I fly on WestJet metal even if I book it through the AA codeshare. I'd need to enrol with AA to collect miles, not sure this is worth it for the one return LAS-YYZ-LAS (unlikely to be flying AA again any time soon).

So it's looking like there's actually no benefit to me to book via the codeshare, unless it definitely allows me through-checking of baggage and booking direct with WestJet wouldn't... (?)