No reads other than he's got a big stack.

Full Tilt No-Limit Hold'em, $1 BB (6 handed) Converter Tool from (Format: Bet The Pot)

MP ($142.50)
CO ($113.40)
Button ($258.65)
SB ($96.50)
BB ($197.30)
Hero ($101.50)

Preflop: Hero is UTG with , .
Hero raises to $3.5, 1 fold, Button calls $3.50, SB calls $3, BB calls $2.50.

Flop: ($14) , , (5 players)
SB checks, BB checks, Hero bets $10, Button calls $10, SB folds, BB folds.

Turn: ($34) (3 players)
Hero checks, Button bets $22, Hero calls $22.

River: ($78) (3 players)
Hero checks, Button bets $65, Hero?

He can easily have an A with A3 and A7.

More likely he has 33 , 77, [Qs], or [Js]

I'm leaning towards fold... have to kinda give credit to the stack and the play.... he could have some random 2 pair as well and even a weirdly played set or running flush or something else that beats you....

actually i'm def folding here without reads he could have 2 3 suited