Sonic would be an awesome character to see in brawl. To my knowledge, Sonic vs. Mario is the biggest in-system rivalry to date. It would be exciting to have them finally fight eachother. But enough off topic.
We can be sure that, asside from G&W who is questionable, every none clone character in melee is bound to get into brawl.
Concerning the clones:
Dr. Mario was a fun character, and it makes sense that the bigger the series on nintendo, the more representation it should have. I would much rather Nintendo give the doctor a complete makeover, although i doubt the possibility of that.
Ganondorf is a given that he will be a completely different character from his melee self, but whatever moves he is bestowed with, he is sure to make the cut for brawl.
Falco and Ganon are the least clonelike of all the clones, and while I am not much of a Ganon player, I can securely say that Falco is much different than Fox, and deserves to keep his moveset the same for brawl.
Y. link is fairly clonelike, but he does have several games and could be given an entirely different moveset, so I would hate for Nintendo to give him the axe instead of taking the initiative and remaking him from scratch.
Pichu evolves into Pikachu, cannot be luigified, and should not return in brawl IMO.
Roy could have been a good character, but due to his lack of popularity he will probably be cut, and personally I would not care if he were cut or replaced.
My final decision: Cut Pichu, G&W, Roy; Luigify Dr. Mario, Y. Link; Allow all others in melee to enter the brawl as they are