This is the roster if NyaseNya, ChaosZero, Serebii, and ShadoXOR are to be believed:
1. Mario
2. Luigi (confirmed by no one, however, I doubt he would be cut)
3. Peach
4. Bowser
5. Yoshi
6. Wario
7. Donkey Kong
8. Diddy Kong
9. Link
10. Zelda/Sheik (Sheik is returning according to ChaosZero)
11. Ganondorf (Ganondorf is returning according to ChaosZero)
12. Toon Link (confirmed by NyaseNya)
13. Samus/Zero Suit Samus
14. Kirby
15. Meta Knight
16. King Dedede
17. Fox
18. Falco (Falco is returning according to ChaosZero)
19. Wolf (Wolf is in according to ChaosZero)
20. Pikachu
21. Pokemon Trainer
22. Jigglypuff (hinted by Serebii)
23. Lucario (hinted by Serebii, and is coming into Brawl according to ChaosZero)
24. Ike
25. Marth (returning according to ShadowXOR)
26. Lucas
27. Ness (returning according to NyaseNya, ChaosZero, and ShadowXOR)
28. Captain Falcon (is returning according ChaosZero and ShadowXOR)
29. Ice Climbers
30. Pit
31. Mr. Game & Watch (returning according to NyaseNya)
32. R.O.B. (is playable according to ShadowXOR)
33. Pikmin & Olimar
34. Snake
35. Sonic.
This is our roster.