I have a ticket booked through UA in business class for cash, YQT-YYZ-ORD-LHR, where only YQT-YYZ is operated by AC, with an AC flight number (i.e. not a codeshare). When I made the original booking was made, AC8306 was a Q400, so was booked into a Y fare code (with fare basis PXNCV5 according to cowtool) - YYZ-ORD-LHR is all P. It has since changed to a CR9, which has a business cabin, so I tried to eUpgrade using the site, but it says ineligible despite being Y - I assume because PXNCV5 is not a Latitude fare basis. Am I boned?

(I thought maybe about calling UA to see if they can put me in business without charge on AC8306 since the fare basis is PXNCV5, but in my experience, agents at most airlines won't do this, even when they're supposed to, and end up messing up the PNR more than it was worth...)