How do you handle second hand to the nuts without a clear read?

Example 1: I have A3d in BB.

Flop comes down Q 3 A, I bet pot, one EP limper calls, turn is a 2, I bet 2/3 pot and limper calls. River is Ace I bet half pot, he goes all in. The only hand that beats me is AQ, but I think he would have reraised me on the flop? My read here is unclear. I called 1/3 remaining in my stack, $35.00, with $170.00 in the pot knowing that he could have AQ but unsure. It turned out he was holding QQ (yes he played it badly).

If you have no clear read and someone raises after you have made a large bet, does any one have a rough guide to the EV of always calling with second to the nuts?