Thanks to PlanetGameCube we are able to report that the Sonic Team announced that Sonic Adventure as well as Sonic Mega Collection will be coming to GameCube

Sega plans to show off Sonic Mega Collection and Sonic Advance 2 at the World Hobby Fair on July 13-14th. Additionally, both games are scheduled to be released in Japan before the end of the year.

The European release date is still to be announced.

Source: Sega Press Release