Hi Cider Monster, you'll find the best cider in Brittany and Apple Brandy in Normandy, but if it's sunshine you want, the further south you head the more likely you are to be sure of the sun.
A lot depends on your ferry crossing: go from Dover to Calais and anywhere on the west coast is a hike and so a drive to the south coast can be considered, but if you're taking a ferry to Caen, Cherbourg, St Malo or any of those ports on the south coast, consider Vendee, Charente Maritime or Aquitaine (listed in order of how far south they are).
There are no guarantees of blazing hot weather in France, but go to any of these regions from mid-May to mid-September and you should do well.
You want to know about campsites - are you staying in a tent, tourer or mobile home?