Oh ho, someone doesn't know his geography, I'm sure these two events need to be separated to make things clearer.
https://en.wikipedia.org/wiki/Battle_for_Caen
I don't know what film festival was going around that time or even if there ever was one, its probably all made up in one of the developers heads.
The Battle for Caen (June to August 1944)
Cannes Film Festival Founded in 1946, the invitation-only festival is held annually (usually in May) at the Palais des Festivals et des Congrès.
So its not the Cannes film festival.