I would suggest the Liberty Tree Tavern at Magic Kingdom.
This is character dining, but they have a traditional Thanksgiving menu I think you would enjoy! If you decide to eat there, I would suggest getting your ADRs (reservations) ASAP because it fills up fast, Thanksgiving is a traditionally busy time at WDW. Call 407-WDW-DINE (939-3463) to make a reservation. You do not need to stay on Disney property to make one.