PAX Prime has already seen a few announcements ahead of the actual event, but according to Larry Hryb a.k.a. Major Nelson, Sonic CD will be playable at PAX, due out on Xbox Live.
The Director of Programming at Xbox Live stated that in a post on his blog, Sonic CD would be at one of the booths, alongside other XBLA titles, as well as Mass Effect 3. Unfortunately no other information concerning release dates is available. Sonic CD was released in 1993, then again in 2005 as part of the Sonic Gems Colletion, however it has been the forgotten game of Sonic’s prime, arguably hailed as one of the best games in the series.
(Source: Gamespot )