If he's 3betting like 30%+ of the time, i think fourbetting wide value range and some bluffs is optimal.

If its like 20-30%, I go for flatting strong hands.

Versus really aggro players the tricky part always is forming weak ranges in good spots. If the guy just cbets and c/f's the turn a lot, floating can be good. If he folds to a lot of flop raises, obviously youd want to raise flop with a weakish range, strengthening your flop flatting range. If he doesnt fold at all and is relentless, then you try 4betting some weaker hands.

Make his aggression as bad as possible by giving yourself the strongest range possible in those spots.