No way to tell, really. I think it varies from year to year, and they seem to like to throw in some randoms here and there (example: Professor Ludwig Von Drake in 2012).
But from my limited experience in Disney races, here are ones I THINK you can count on:
- A character in front of the Lunching Pad in Magic Kingdom (Buzz, Stitch, Space Pluto or Space Chip and Dale??)
- Characters in front of the Mad Tea Party (Alice, Tweedle Dee & Tweedle Dum or Mad Hatter??)
- Characters in front of the castle (Lady Tremaine and step-sisters? Prince Charming? Suzie and Perla?)
- Characters at the finish (most likely a classic - Mickey, Minnie, Donald, Daisy or Goofy)
Those are complete guesses...just what I've seen running races myself and reading other reports. And that's a bare minimum list...you'll see the most characters in Magic Kingdom and lots of others as well.