We were in Nice on a Sunday--in fact it was EASTER Sunday--in 2002 and were very surprised that shops were open even in the morning, and restaurants weren't crowded. I have no idea if this is a generally true, but at least you don't have to rule it out.
I've been trying to find a rental car in LeHavre on a Sunday, without any luck. Tried all the major US ones that are there, EuropeCar, etc. Anybody know of any other one's I should try for a rental on a Sunday in LeHavre?