Playing in a 1-3 game yesterday. I have been pretty active, and in cases where I have shown down, my hands have been good, top 20% or better in starting hands. I start the hand with around $330 in my stack. After multiple limpets, I raise with A ♥ A ♦ on the button to $18. I get 3 callers. Flop comes out A ♠ 3 ♠ J ♠ It is checked around. I decide to bet out on the flop with a bet of $45. It goes fold, fold and the cutoff thinks for a short time and shoves all-in for around $300 give or take. He has me covered. He has been a pretty active player to this point with a pretty wide range of hands.
What's the move here? Fold or call?
With no rise pre flop, he could have a flush already with something like 9 10 of spades, but why raise so big. After I've been the aggressor and raiser preflop? I'm thinking he has a hand like KJ of spades or QJ of spades, giving him middle pair and a strong redraw to the flush. But I would think with those holdings, he might want to peel another card and see if he can get there without getting blown off the hand. Any sets are no good for him. Is there a part of his range here that I'm missing?

Also, in multiplayer pots, I have really profited from leading out when I do hit my sets, especially on the flops that bring draws and I'm with aggressive players. In this situation, do you have any suggestions on the flop bet? Too big? Too small? Or is a check the better move here?
Thanks,
Angell