the Gorges du Verdon are rather spectacular and Moustiers-Ste-Marie would make for a pleasant en route stop. Can't really recommend anywhere to eat there as it has been many years since I last was there.

It does mean a detour compared to the direct Cannes-Aix itinerary, though. Probably not much more than Cassis in distance but certainly in time, as it would mean driving on slow and winding (albeit beautiful) roads.