flat calling with quads on the river

[hate_dr_dre]

alright, so I was in a hand at .25/.50 fixed o8, and villain's play tilted me because it was so bad. I don't have the hand history but I have the general points that matter, so hopefully I can get some decent feedback on this.

I have A3xx utg, villain 1 has 88xx on button, villain 2 has a3xx in CO.

flop was 8 8 6 T 2 (I can't remember how the betting went up to the river, but I don't think it's necessarily incredibly pertinent to my point)

I led river (put CO on a2xx, but i was wrong), CO reraises, button flat calls, I call.

The question was, wouldn't a 3-bet with the nut high be the perfect play here? Villain argued he flat called to trap in my last bet, and that if he raised I might have folded. I countered that if he 3 bet and I did fold, CO has to call for 1 more bet which would have been the bet he was hypothetically losing from me. By 3 betting, he basically would have had a freeroll to another 2BB in the pot, at worst his 3-bet would have the exact same result of just calling.

thoughts?