Not sure what Bose-X had in mind, since Rennes isn't really in Burgundy.
There are two Aeroclubs at Rennes.
Aéro-club Rennes Ille et Vilaine and Rennes Air Club
Rennes, as you will have gathered is a large-enough airport that you don't need to worry about speaking French to the controllers although from previous experience, a little French will go a long way with making friends in either Aeroclub.
Of the two clubs, Aéro-club Rennes Ille et Vilaine is probably the best to head for. In addition to the usual Pipers and Cessnas, they also fly Grobs and a Piper Cub and CR100 if you want to go upside down.
Details on their own site:
http://perso.wanadoo.fr/acriv/index.html