4betting, while I'm not thrilled to do so, seems better than the other options. You say MP is kind of fishy, and he does have a high enough 3bet % that we're ahead of him, maybe 3:2 or so. CO is loose passive, but even so, how likely is it that he'd flat with a hand that's ahead of ours? Best guess at his range is something like middle pairs plus big aces.
Folding seems overly conservative, and if we call, we have to expect a large majority of flops will include at least one over, which fits MP's range much better than ours. So if we call pre-, we're effectively set mining or will be looking at leading the flop into 2 opponents.
Considering all this, I'd rather 4bet.