Probably Ted Cruz, Jeb Bush and Mitt Romney. I think that Scott Walker, Chris Christie and Rand Paul will run as well, though they will probably just win their homestates and nothing else.
You have to consider the calendar though. For instance, isn't the Kentucky primary almost always held in May? I can't imagine Paul would stay in that long if he was shut out completely in the 40+ states that voted prior to it.
Anyway, I'm not going to guess this yet since there's way too many variables. But I think the maximum is probably 3 different people, due to the fact that it's difficult to stay viable without winning at least one of IA/NH/SC.
