Alright, here's one I haven't seen for some time.

Need to book a YYZ-SFO (OW) Nov 17 ideally, but 16th could work or maybe even 18th. In the past, at least when I've looked, UA and AC seem to almost always price the same (obviously, AC-operated flights show up on UA.com, and UA flights also on AC.com), with basic at the same and regular Y on UA pricing the same as AC standard. Today, was looking as I noticed AC is having a sale, but UA is not matching the price. AC, for example, is selling AC745 for $211 in Standard (no basic fare being sold), but on UAs website, UA is selling UA8433, which is the codeshare for AC745, for $276 in regular Y (and also selling a basic fare for -$20 - no thank you). The AC fare is booking into G, the UA into K, even though expert mode shows G6 (which is how many seats AC has for the lowest price).

In my experience, at least on this route, quite odd for UA and AC not to have the same pricing. Maybe I just don't look often enough, and what I am taking as the norm just isn't. Any ideas? While booking through AC will I guess get me more RDM and PQP, would much prefer to book even AC flights via UA as I have FFC I'd like to use, but even beyond that, there are no change fees (AC does unless I book into flex at +$100), and if I need to cancel for some reason, much easier and more flexible to use credit than on AC.

Also very odd to see the pricing on UA vs. AC metal. While many of the AC-operated flights at what I would call a 'normal' range (~$200 - $300), many of the UA flights that weekend are in the $500 - $600.