I have read in Rick's guidebooks that on June 21st there are music festivals everywhere in France. We will be in Provence/Cote D'azur. Our itinerary is still flexible. Can you recommend 2 or 3 towns for the best events? (Not Nice or Monaco as we will already have been there)
On the 21st, the music is everywhere. It doesn't matter where you are, there will be music: parks, cafes, beaches. No one knows what will be played or who will be playing in any particular town, at any particular hour. The larger the town, the more music. Just walk around.
It's a great night to be in France. You can scope things out the day or two before by checking for signs showing where streets will be closed and/or stages being set up. Make your restaurant reservation in advance as restaurants fill up on that night - especially if there's outdoor seating where you can hear the music.