Hej,
You can have a look at the following web site:
http://www.directwind.com/lien.php?lien=spots.htm
There is a description of most of the windsurf spots in France. Of course, it is in French, but if you plan to go there, you sure have to speak French!!!…
I used to go to la Tranche-sur-mer and Hourtin in the summer. They are two very good places for sea breeze (usually you get 8-10m/s in the afternoon). June is probably a very good time for sea breeze (in July, it can become to hot and dry, and the sea breeze effect does not work any longer).
I am not a wave rider at all, but I know two very good places for wave riding: La Torche (Bretagne) and Wissant (Nord). Anyway, the website is rather well documented. If you have any question, just drop me a line at:
demaz@nephy.chalmers.se
Best winds
Christophe