And possibly Matt Damon....
True, but Matt Damon hasn't been in all his films.
Ben Affleck, I'd say is almost guaranteed (he was in every movie since Mallrats, and played the leading role in half of them)
Jason Mewes, almost guaranteed
Brian O'Halloran, almost guaranteed (he's never failed to be in a KS movie)
Jeff Anderson, I hope. He's my favorite actor in any KS movie
Matt Damon, likely, but not guaranteed
Bryan Johnson / Walt Flannigan, I hope they make an appearance. "You tell 'em, Steve Dave!"
Scott Mosier, almost guaranteed to produce it, and I'm sure he'll make a cameo appearance
Other than that, and that Kevin Smith may also make an appearance, I'm not sure who else to expect. But I imagine the cast will mostly be made up of his friends (ie, the people above), since they work for fairly cheap and they're great actors.
I also wonder if Jay and Silent Bob will be in it. After Jersey Girl, he said that he would never make another movie without Jay and Silent Bob, although he may have been joking.