2nd hand at new table, no reads on villain

PokerStars No-Limit Hold'em, $0.25 BB (6 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

Hero ($23.80)
SB ($20.95)
BB ($26.35)
UTG ($59.90)
MP ($25.70)
CO ($17.15)

Preflop: Hero is Button with A, K.
3 folds, Hero raises to $1, SB calls $0.90, BB calls $0.75.

Flop: ($3) 3, 7, A (3 players)
SB checks, BB checks, Hero bets $2.25, SB calls $2.25, BB folds.

Turn: ($7.50) J (2 players)
SB checks, Hero bets $5.75, SB calls $5.75.

River: ($19) 8 (2 players)
SB bets $11.95 (All-In), Hero ???.