Sounds like a fun trip. Remember to take some pictures to show us.
The aircraft has either a continental or lycoming engine, yes? So vintage or not, same situation as any other certificated light single. I fly our cub in straight lines, water not being any more dangerous than large forests or steep hills.
Have a nice bimble and a good time with the family. Remember that many French airfields have grass as well as tarmac runways, sometimes theoretically reserved for home based aircraft but in practice often available on request. Take a PLB and wear your lifejacket where appropriate. I don't think there is a suitable dinghy available for a cub.