Air Canada is definitely not being transparent with the upgrade process. My partner (Elite) was waitlisted for an upgrade from SCL to YYZ. When he got to the airport he asked the agent about his chances. She said that chances weren't that good but she gave him the option to buy a LMU for 800$. Because he was travelling all the way to LHR he accepted it. The worst part is that she didn't remove the upgrade request from the reservation. Consequently, because he ended up flying in C, his credits (17) were never returned to his account.