My range goes all the way open with 3 players. You're either a blind or the button, so I open with my entire button range, which is about 54% of hands.
Looks like this:
"Big" Card: K7+, Q8+, J8+, T7+
Suited cards: A2s+, K2s+, Q7s+, J7s+
Suited Connects: 23s+
Suited 1 gaps: 24s+
Suited 2 gaps: 25s+
Offsuit SC's: 65o+
Offsuit 1 gaps: 57o+
The other thing I may play are 26s-T6s which aren't in the initial range
I still don't want to be mixing it up oop that often, and I will open up my 3betting range as defense, if my opponent is opening a wider button range. But I'm not 3betting hands like KJs, KQo, things that can really screw me in a 3bet pot. I'm 3betting TT+, AK, maybe AQs/KQs, 86s, 74s, small sc's and gappers. I'd rather call with my hands like KQ, KJ, KTs which have significant equity against my opponent's opening range, but then become crap when he's willing to call my 3bet or 4bets me.