There was a time when Aeroplan tickets booked as business awards were highest priority. Then they were demoted. I don't remember if it was in two steps, first to lowest priority, then to no possibility of upgrades.

However, if you dig deep enough into this forum, you will recognize that for quite a while, there was no possibility of "upgrade" on aeroplan tickets. More recently these came back. Again, it's well documented here. Pretty obviously, at a low priority. So as not to compete with upgrades for FFs. That also is well documented.

Not an official confirmation; form AC's standpoint the priority list is apparently something liek a trade secret. However, from the experience reported here, it's very clear that these are at the bottom of the list.

As they should, BTW.