I am in the same situation as yours. But I choose to let my 2 boys continuing in French school here in Ottawa.
The reason is simple, as you may know, French is minority here, if you want to have a solid French, the French immersion program will not achieve the same goal.
Many parents told me not to worry about their English learning because they grow in a English environment. Their children are perfectly bilingual. On the other hand, if the kid's French is solid, it will be even easier to pick up English.
So is up to you to think about that.