Sonic has not been even suggested for SSBB, but Fox has, he is for sure in it...
http://media.wii.ign.com/media/748/748545/vids_1.html
these videos have all the confirmed characters so far...what isn't in the videos isn't in the game...yet
Y'know what'd be cool, though? the ability to use Miis in the game...you'd put your piece on the Mii character, and then you'd be able to choose Miis from your Wii. That'd be cool