Guadeloupe is not an official member of FIFA as a federation, so it cannot qualify or compete at FIFA World Cup or Confederations' Cup. It's just an extraordinary CONCACAF member and its Caribbean branch (CFU). Therefore, Guadeloupe only competes in CONCACAF Gold Cup and Caribbean Cup. Moreover, footballers who play for Guadeloupe or any other French overseas territory (like Martinique) are still eligible to play for France any time they wish.
That said, you can just keep his nationality as French for the time being.