Have struggled thru this entire thread and "get" the issue with all such codeshare segments USA-Canada -- the deep uncertainty and difficulty of reconciling the two plans. Until the last few entries though, I thought the solution for MP earning was pretty simple: just book on AC site with Flex fares and you should be good. So, for my target nonstops, no problem apparently; Tango fares already exalted, so the extra for Flex hardly matters.

Now it seems, not so sure this is right; too much arbitrary and capricious shape-shifting by AC, last-minute and with no notice, even after ticketing. Not good; I think I'll need to find another routing, even with the inconvenience of connections and on some other carrier where earning won't really mean much for me.

As an aside, I only considered this as a paid itin. as it seemed the only way to get onto the flights I wanted, the two AC codeshares sold as UA 8346 4/30, and UA 8675 5/4. They can be purchased as Flex with presumed earning on MP, and yet they do not show up as AWARD options for MP. That seems very odd to me -- if they are indeed codeshares, can/does AC still block them for MP award travel, or is there something I can't see at UAL.com that an agent can see, maybe I need to phone. PS no status here but I don't think that should matter so long as I have sufficient miles to book the award...