If they're purely unveiling characters at events, we won't know the full roster before release, I don't think. And taking into account any characters they might wanna keep secret, we definitely won't know it for a while.
Currently, there are 10 confirmed characters, with like 3 or 4 we know are coming. Beyond that, there'll probably be around another 6 or 7, but we don't know for sure.
Awaiting: GW2, Bioshock: Infinite, The Last of Us, GoW:A, Playstation All-Stars, AC3, Watch Dogs, Beyond. PSN: Ambulance-Chaser