Could 3 bet or flat, I'm feeling very comfortable at the table and playing in position vs this deepstack.

OR stats: 41/28/18 over 500 hands
SB stats 74/6/1 over 550 hands

Sometimes I raise here partly for value but more to slow the action and give my opponent a hard time. Against the same opponent I had flatted AA pre and raised a similiar board to his lead, but he just clicked it back which I folded to (we were very deep again)

Turn is the best card in the deck!
I was really tempted to flat his raise to under-rep my hand massively...but it is quite vulnerable, do you think it is good to flat to let the SB play also (he is very weak player and could come along with a big range + sweeten the pot even more) and maybe get more $$$$ out of the OR on later streets, or raise to get HU / build pot for value (he could jam if I'm lucky) and to protect my hand.

After he checks I had a hard time deciding on the best bet sizing, potting is an option to make my hand look like a missed draw.
However I think he most likely has missed nut draws (ax spades or QT9 combos)

If he has JJJ I think he will call the river regardless of sizing...I think it is quite unlikely he does as there is fewer combos of JJ and he probably gets more excited on the turn with it.

Otherwise I was thinking a smaller bet that is still quite substantial (like 180) to still represent a bluff and give him an opportunity to check-raise (i.e. enough room for him to think I can fold). Not sure whether he is capable of this though.

What do other people think the best bet size is on the river and why?