FWIW - when I last used reward travel for my wife and myself in Executive class last year - at time of booking they did not have reward seats avail on the return leg, but we took the flights anyway return to Fort Lauderdale. They indicated that they would place a comment in the record and that we should check at the airport when we return back to YYZ from Fort Lauderdale ... sure enough at the airport we checked in - asked about upgrades on the reward travel, they read the instructions and we got the seats ... so keep the faith - just make sure that AC places information in the record - the SE desk did it for us and actually placed instructions for the check-in agent on what to do to make it happen.

Good Luck

SimonC