From NeoGAF user Steve who bought the latest Game Informer that ran a feature on Resistance 2. He states that the game will be a
"HUGE cooperative game... EIGHT-PLAYER story-driven campaign along side single-player campaign. SIXTY-PLAYER Competitive modes... HUGE United States Landscapes as backdrops. It will have huge boss encounters with 8 player co-op over PSN and 2 player local co-op."
Well known user JStevenson from NeoGAF who is an employee of Insomniac has confirmed the information to be true.
Update 1: Its is also revealed that the game will release in Fall 2008.
Update 2: Here is the link for the magazine scans: