Originally Posted by yyzgigi
Once the return flights were available, pay to change the earlier flight from CDG-YEG to your desired date after your departure date. As I'm not sure that AC will allow you swap outbound and returned on a dime you should confirm in advance (not sure if anyone else has experience).
Policy has recently been revised such that you can book your outbound flight and add your return flight for free if your return date is not yet in the system when you make your intial reservation. This applies to AC rewards only. Note that when you add your return date and there's no availability, cancellation fee will apply if you decide not to proceed with the trip because there's no return availability. This will save you from having to book a return date which you have no intention to travel and then pay the change to change to your desired date once it's in the system.