short stack was a donk and mid-stack was unknown. The pot was pretty big. Double barrel or check /fold ? If we bet, whats optimal bet sizing?

PokerStars No-Limit Hold'em, $1.00 BB (8 handed) - Poker-Stars Converter Tool from FlopTurnRiver.com

UTG ($52.55)
UTG+1 ($17)
Hero (MP1) ($100)
MP2 ($139.30)
CO ($60.10)
Button ($18.90)
SB ($37.65)
BB ($160.25)

Preflop: Hero is MP1 with 7, 7
2 folds, Hero raises to $3, 1 fold, CO calls $3, Button calls $3, 2 folds

Flop: ($10.50) 5, 4, 5 (3 players)
Hero bets $6, CO calls $6, Button calls $6

Turn: ($28.50) 5 (3 players)
Hero ?