This is a 3bet pot button vs SB right? even with 6% this is gonna be an easy call down, this is the perfect spot for him to go for a 3 barrel bluff. Never folding

Agree with previous! You are seeing ghost if you are afraid here

Also. Would be quite bad if we only continue with quads

From memory I think a 3.5% 3b is pretty much always AAxx. At 6% he can have some other broadway runs. I would call turn call river. If he pots river likely he has AAxx, but I think we just call and hope he has the AKxx. He can have some kind of double suited AK4x combo also but this is very unlikely. I dont see value in raising turn.

Some AQTJds type combos are also possible.

Aces are 2,5% of all hands. So if someone's range is all AAxx it will be 2,5%. The thing is that even if someone has 2% or 3% 3bet, it doesn't mean it's Aces. 6% from 300h sample size can mean that he has 3bet less than ten times in total. We can't make big assumptions unless you have exact information about the hands. If he has 3bet ten times and you have seen each of those and they are Aces, then there is a likely chance that he has Aces.

On the other hand, if you think his range is Aces I don't think you can call preflop. So as you call, you should think that his range is a lot wider than Aces. Ace on the turn makes them even less likely.