Hi
I dove in the
Marseille calanques, namely in Niolon, but that was with a French type of YMCA, so not an option for your client. If you google "Club de plongee Marseille", you'll find many options, both on the continent (there's even one in the old port) and on the close-by Frioul island.
Everyone on the French dive forum (plongeur.com) recommands this club :
Plongée Passion Carry-le-Rouet Marseille
It's located West of Marseille itself and I've never been there myself, but I will definitely check it out as soon as I have a bit of time and money.
I also dove the
Hyères islands (Port Cros and Porquerolles) with these guys two or three years ago, they were great and are supposedly the best in the area according to plongeur.com :
Aqualonde Plongée - Bienvenue sur le site d'Aqualonde Plongée
I don't know if they accept Padi divers, so you should drop them a mail.
Only downside is that they're located in a small town, so not much to visit or do besides diving, laying on the beach or going out to cafés and restaurants, if he doesn't have a car.
Now, if he does rent a car and is also interested in visiting the French riviera, here's an option : in a week he could very easily dive Marseille, Hyères, Cavalaire and Nice.
Heard good things about Cavalaire but don't have any info.
Spent a week-end diving in
Nice, beautiful town, saw many groupers and squids, I personnally didn't like the dive op I used (Nautile), but there are at least two others right on the old port, a very convenient location.
Hope that helps, let me know if you need more info.