That kinda situation sucks. If you don't have a real read on him, I am compelled to call, but that might be a leak on my part. You might have the best hand often enough, but even if you don't, other player might try to bluff you on rivers if you fold. It does not fit why he would wait till the river to raise. If he had a good ace, why did he not check raise you on the turn. Then bet out the river. If he had pocket Aces he slowplayed, but that is strange. If he opened PF with 2's or 4's wow!

When in doubt call it down if there is some doubt.