Hah. Well, short answer is - I don't know.

I had been shying away from the COPA flights, because...737, and an extra stop in PTY. In your case maybe it's not an extra stop for you (stop in PTY instead of BOG).

I have not done extensive research about the quality of COPA's 737MAX lay flat seats. I've been in enough 787s with herringbone seats like Avianca's to feel confident about the seat comfort, and for me, seat comfort trumps almost everything else. I can feed myself (or grab some takeout) airside in LAX before I board, and I'll manage just fine without the champagne or bling (of course, if it's on offer...).

I'd take a hard look at refundability and what happens to your miles/fees. United's policy is quite consumer-friendly, I don't know much about Air Canada's. I hate leaving points orphaned and scattered around, they can so easily vanish eventually, even if they won't for a while - stuff happens (see "pandemic"), plans change, etc. I'd also read more reviews of COPA's seats to get a clear picture of their strengths and weaknesses (though I was happy enough to book them for my return from Colombia, but in my case the Avianca 787 was not an alternative, but going through Miami on older 737s was the alternative).

Of course, if you dump your Avianca booking, then the next day they will probably put a new 787 into service on that route, so you'll be doing me a favor so thanks in advance for taking one for the team. Good luck whatever you end up doing, it's always an adventure.