The domain names sonicadventure3.com, sonicadventure3.net, sonicadventure3.org, sonicadventure3.info, sonicadventure3.fr, sonicadventure3.eu were discovered by the French division of 1&1 Internet, reports TSSZ.
The URLs lead to a default landing page not associated with Sega, perhaps suggesting that the registrations are unofficial.
Previous registrations, meanwhile, were handled by EuroDNS, where the likes of Sonic Generations, Sonic the Hedgehog 4 and Sonic Free Riders remain to this day.
If true, the game would provide a sequel to Sonic Adventure 2, which was originally released on the Dreamcast in 2001 and introduced Sonic's rival Shadow, while allowing players to go through both light and dark storylines.
Details of a re-release were leaked in June when a listing for the game surfaced on Xbox Live, before being pulled.
The original Sonic Adventure received the HD treatment for the same platforms in the autumn of 2010.
Sonic Adventure 2 is expected to be released for Xbox Live Arcade and PSN in October.
Watch a gameplay video from Sonic Adventure 2 below: