While it's clear that they will be showing Mass Effect and Sonic RPG at the expo, PSU is speculating that they will also be revealing a new PS3 exclusive. Their reasoning stems from a conversation with Richard Vogel, Bioware's Director of Operations, at the GDC, during which he mentioned to PSU that there was a game in development for the PS3. Unfortunately, no further details were able to be obtained.
Checking the Bioware website, the "in development" games list shows a listing for a "new next generation game". We look forward to seeing if PSU's hunch is correct when E3 comes around.