NL100: Set facing river check raise -- bluff or monster?

[Bianculli]

Villain is 18/7/1.6 over 71 hands. Haven't seen anything unusual.

Full Tilt No-Limit Hold'em, $1 BB (9 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

saw flop|[color=#C00000]saw showdown</font>

MP2 ($19.05)
MP3 ($100)
CO ($44.75)
Button ($140.10)
SB ($19)
BB ($137.45)
UTG ($161.05)
UTG+1 ($90.60)
Hero ($294.95)

Preflop: Hero is MP1 with 7, 7.
2 folds[/i]</font>, Hero raises to $3.5</font>, 5 folds</font>, BB calls $2.50.

Flop: ($7.50) 7, A, T (2 players)</font>
BB checks, Hero bets $5</font>, BB calls $5.

Turn: ($17.50) 6 (2 players)</font>
BB checks, Hero bets $10</font>, BB calls $10.

River: ($37.50) J (2 players)</font>
BB checks, Hero bets $20</font>, BB raises to $75</font>, Hero???