[djk123]

I think reraising is perfectly fine here only if you are planning on calling a shove.

I prefer raise/calling over flatting for a few reasons:

1)OP noted that this raise was villain's 3rd in 6 hands, so clearly villain is aggressive and opening a wide range of hands.

2) It's a CO open, BU 3bet situation. In today's online poker world, CO opens don't get too much respect, and thus BU 3bets of an aggressive player's CO open are not perceived as strong as they were in the past, which means villain is not necessarily folding AJ or even AT. They are playing 8 handed as well if that matters at all.

3) Villain's history of only playing large buy-in tourneys suggests, although obviously doesn't guarantee, that he or she is aware of resteals and possibly even capable of 4 betting light.