I don't think that you should have a problem with First class on the European flights as I understand it usually goes after business.

However, if you are really concerned and want to protect yourself, in theory if you were willing to accept the change fees you could get the following:

early date: CDG-YEG
desired departure date: YEG-CDG

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).