Too little details to say that this was Bully 2 or even a canned project. Could have just been a DLC pack for GTAV or another project. I find it extremely suspicious that they were in the casting stages and
poof it's been canceled, especially when he would have likely been just recording a pedestrian voice which are usually recorded much later in development. My money is more on a project that has been delayed or they just didn't need/want him anymore and he took it as it was canceled.
Find it interesting that he's supposedly been excluded from the credits of Rockstar's games. If you watch the credits, there's a huge wall of voice actors for pedestrians.
Agent: This game looks really good and has been in development for a while, this might of been canceled due to the fact that it is an old game and releasing a game with graphics that old in this time period might be a bit... bad.
Agent has been in production/tossed around in some form since 2003. To my knowledge, aside from a couple of ports a long time ago, Rockstar has never canceled a game after announcing it. It's obvious that Agent is a game that Sam and Dan really want made, otherwise they would have canceled it before announcement just like "We are the Mods" was.