darkling is right, of course the next game (if it got made) would be titled Baldur's Gate 3. It might have a sub-title as well, for example, "Baldur's Gate 3: The Wizard's Tower". And it could have absolutely nothing to do with the the original Baldur's Gate story, but just set in the same world of Forgotten Realms with a brand new story, but it is very likely they would use the Baldur's Gate name for recognition and to help the sales.