Miyamoto and Sakurai already said they really want Sonic in Brawl and Miyamoto (creater of Mario) said he would be the best 3rd party addition to the game. Countless times have they asked SEGA to allow and at 1st they said no. That was back in June of 2004. And again in May 05. Has SEGA said anything sense? We, the public, dont know. If they have, than its a big secret. Cause SEGA keeps saying 'No' to the public and Nintendo doesnt say yes or no. Id have to guess that Sonic is In Brawl, cause if he wasnt Nuntendo would have said so already, no point in letting the public up for nuthing. And Im pretty sure they wouldnt leed us to believe Sonic is in, just so that we buy the game, even if he isnt. Id expect that from Sony, but not Nintendo.
SEGA i dont know about, their bad at keeping secrets, Id guess thats why they just say 'No'.
Miyamoto would love to see Sonic in Brawl, but Sega hasnt given them the okay hand.