I'm traveling transborder for the first time since the start of the pandemic, and I was looking at booking ORD-YUL (paid economy tickets). At first, my initial travel dates were outbound 06DEC, return 12DEC. UA shows a couple of UAEx CRJs (they almost never fly anything larger than a 50-seater on this route, which is annoying, but I digress...) and an Air Canada Jazz 175. The return showed just a single CRJ on UA.

Later on I went to Air Canada and noticed that they actually have several flights on 175s and CRJ900s, as well as selling UA's CRJ flight. The return had a couple of Jazz 175s on top of the UA flight (and, in that case, regardless of my aircraft preference, Air Canada's flight was timed much better for my needs).

My outbound date wound up changing one day earlier, and again, UA is only showing their sole CRJ for the Sunday, whereas Air Canada has 2 or 3 extra flights of their own.

I would up booking direct with Air Canada because there's no way to get the flight times I prefer when booking through UA. As it has been a couple of years, I don't remember if it was always the case that UA showed a more limited selection of ORD-YUL flights, but given the extreme lack of frequencies at the moment (not to mention the fact that what's left is on CRJs; at least an EMB-145 would be moderately tolerable), it really makes it appear as if there isn't much availability in that market if you're just looking at UA.

Anyone know why UA would only codeshare some, but not all of the ORD-YUL frequencies, and none on Sunday?