I don't know man, he has all the flopped straights, all of the flopped/turned sets, turned straights and probably at least one combo of a worse flush on the river. I don't know if I can fold against an aggro who I have some history with. BD flush has to be kind of unlikely in his eyes here so I can see him jamming his 9 combos of straights since you can potentially raise/call a set/lower straight here.

Doingg some handreading this do look like Ax in spades. I would heavily discount flopped straights and sets regarding flop action alone.On the River he could do it with the lone Ace of spades . Against passive or nit I fold, otherwise call.

He have 7 better combos and our pot odds (I haven't do math precise) ~36%. We need around 5 bluffs (4 and something to be more accurate). Something like AsJ ,AsT and AsK possible candidates.
Some people honestly will over bluff here bunch and calling any flush is +EV. Your flush isn't matter you are doing same thing as 43s which is blocking his Ace of spade flush.

You are playing a 4-handed game.
Probably in a non-standard site.
I'd say that you find some players over value betting some hands in this board.
If we assume that he has just a few worse value combos, we may find a call.
Nevermid. I was writting this imaging the spot as 100bb deep.

Now I'm not so sure about how people can bluff in these spots.
Probably really underbluffed spot given that villain is shoving OTR and preflop you were around 200bb deep. As you said, on this flop, most of people perceive that it is a good board for the preflop aggressor. At the same time he might choose to check some weaker aces, right?
Then, as you mentioned in your post, it seems more likely to see a bet from some backdoor spades, but at the same time, weaker AXss can follow the line it went.
Hard to fold, unless villain is capable of bluff this deep. And IMHO, at micro limits, most players are not capable. Fu** I feel some bad thinking about this hand, really hard for me. probably just fold and move on.

Well thanks guys, honestly afterwards I think that we need him to have bluffs here to be able to call it down, even if we beat some value hands. I tend to agree with weltcheftrainer that amongst his range, small Axss is the kind of hand that occurs the most here. I ended up calling and villain showed A3ss