There were some rumors that GTA III and VC were rerated in order to be re-released as PS2 Classics on PS3, but there were no new information since then, so it's hard to say anything.
And about these games on XBL:
|QUOTE (Asked & Answered: Max Payne 3 and Grand Theft Auto V)|
|Due to compatibility issues and other technical limitations, we do not have any plans to make Grand Theft Auto III or Vice City available on the Xbox LIVE Marketplace.|
Link to this page: http://www.rockstargames.com/newswire/arti...eft-auto-v.html
Note that you can run GTA III and VC on your X360 as a Xbox Originals