Actually AC has been really good on those companion tickets. Even though they have not allowed upgrades at time of reservation, they have always upgraded my companion, even when he/she was not travelling with me (ie different return dates). We just talked nicely to the agents and Voila! I don't expect it but it has, so far, always been a positive experience.

But remember it wasn't just the companion ticket, the first booking took considerable time and for the Calgary agent to spit out MY ticket, took the a significant part of the time in Calgary. Then she worked on the companion ticket. I could go into excruciating detail on that process (we are supposed to be on the same itinerary, but somehow she got us on different ones) but won't.