
to the disboards!
Dining reservations open up 180 days in advance so pretty much all of December is already booked. Character meals are very popular so they will be harder to find, but cancellations will come up because of the no show penalty which most want to avoid.
Many find openings closer to their trip days, but keep checking online multiple times a day because cancellations can occur at any time. You can also subscribe to the December cancellation thread at the top of this forum, but be sure to read the rules in the first post. Also, many have had success with the reservation finder on the Touring Plans website.
It helps to be flexible with the time you want to eat so check for non-peak meal times (i.e. lunch before 11 or after 1 PM or dinner before 5 PM or after 7 PM) and at restaurants where there are characters at all meals (e.g. Garden Grill, Tusker House, Crystal Palace) look for times for all meals.
There are character meals in each of the parks, but you can also try to combine a day at a park with a character meal at a nearby resort if you cannot find a reservation at an in-park restaurant (e.g. Magic Kingdom day - Chef Mickey's at Contemporary or 1900 Park Fare at the Grand Floridian), Epcot or DHS day - character breakfasts at Cape May at the Beach Club or Trattoria al Forno at the Boardwalk).
If you go to the parks at opening and go on rides and attractions the first two or three hours when the parks are less busy you can then book a late breakfast/early lunch.