Liberty Tree Tavern in MK! The Patriot's Platter is all you can eat turkey, pot roast, roasted pork, mashed potatoes, veggies, stuffing and mac and cheese. It's delicious!
LTT is the obvious choice. And its good comfort food.
We have done California Grill twice and loved it. Did not have anything close to a traditional thanksgiving dinner, but it was really good.
We had Thanksgiving dinner at Grand Floridian Cafe a couple years ago. It was fine. If you can't find any ADR's this late in the game, I'm fairly sure all the counter service restaurants will serve turkey dinners. They are fine too.
If you are talking about this year, then you are way too late. All the good restaurants get booked for Thanksgiving Day at the 180 mark. If you are talking about next year, then you will be good to go. We have done LTT, Boma and Le Cellier all on Tday and enjoyed them all.
Don't give up hope though. This is fast pass week for Thanksgiving. People are changing their reservations around. You should still be able to get something you would like.