There are only 5 hills on the marathon course:
1. The overpass climb up at about mile 5 just outside EPCOT
2. The underpass climb out by the Contemporary, mile 9.9
3. The 2 overpasses between the Animal Kingdom and the turn around, miles 19 to 20
4. The slanted overpass just pass mile 22, as you climb up and bend right to enter the Studios.
The rest of the course is flat. It may not seem like it when your legs are blown, but it is. If you'll be in the Animal Kingdom area the whole distance, it will be flat city.
Good luck