100NL hand reading hand

[McStinky]

Villain seems to be a pretty solid aggressive player. Have been playing with him for a while and haven't noticed any mistakes. I know I am getting good pot odds on the river, but is there really anything he can have that I can beat? On the other hand, is there anything he can have that I can't beat? Is there anything he could have at all, besides 45? How did I do up to the river?

Poker Stars - No Limit Hold'em Cash Game - $0.50/$1 Blinds - 6 Players - (LegoPoker Hand History Converter)

SB: $216.80
BB: $68.85
UTG: $142.70
Hero (MP): $174.70
CO: $203.20
BTN: $175.75

Preflop: Hero is dealt 3[img]/images/graemlins/heart.gif[/img] A[img]/images/graemlins/heart.gif[/img] (6 Players)
UTG folds, <font color="red">Hero raises to $3.50</font>, CO folds, BTN calls $3.50, SB folds, BB calls $2.50

Flop: ($11) 3[img]/images/graemlins/diamond.gif[/img] J[img]/images/graemlins/club.gif[/img] 6[img]/images/graemlins/heart.gif[/img] (3 Players)
BB checks, <font color="red">Hero bets $8.00</font>, BTN calls $8.00, BB folds

Turn: ($27) A[img]/images/graemlins/spade.gif[/img] (2 Players)
Hero checks, BTN checks

River: ($27) 2[img]/images/graemlins/spade.gif[/img] (2 Players)
<font color="red">Hero bets $20.00</font>, <font color="red">BTN raises to $50.00</font>, Hero?

Pot Size: $127.00 ($3 Rake)