just IMHO, the French Atlantic bases sank any collaboration with the Vichy regime? ("they're not going anywhere") and proved to be something of a mirage as Allies developed ASW and shot up the departing uboats.
so if they built as originally planned in Norway, they are only part the way to cracking the GIUK Gap? they need a waystation , clandestine meeting point? therefore my suggestion of Greenland, also the cryolite mine there was crucial to US aluminum production at the time.
the whole idea is just speculative fiction, the few aircraft they had useful, HE-119, ME-261 were limited, specialty types, and the tanker uboats not even conceived pre-war? however it resembles Narvik in that defenders would be difficult to evict?