BTN: 212.75 BB (VPIP: 23.78, PFR: 15.44, 3Bet Preflop: 6.27, Hands: 1,372)
SB: 95 BB (VPIP: 42.65, PFR: 25.37, 3Bet Preflop: 14.22, Hands: 549)
BB: 78.49 BB (VPIP: 28.01, PFR: 16.78, 3Bet Preflop: 7.38, Hands: 2,142)
Hero (UTG): 219.88 BB
MP: 40 BB (VPIP: 27.75, PFR: 8.64, 3Bet Preflop: 4.27, Hands: 385)
CO: 302.63 BB (VPIP: 56.73, PFR: 16.35, 3Bet Preflop: 10.87, Hands: 106)

SB posts SB 0.5 BB, BB posts BB 1 BB

Pre Flop: (pot: 1.5 BB) Hero has 4 K J A

Hero raises to 3.5 BB, fold, CO calls 3.5 BB, fold, SB calls 3 BB, fold

Flop: (11.5 BB, 3 players) 3 9 4
SB bets 10.86 BB, Hero calls 10.86 BB, CO calls 10.86 BB

Turn: (44.09 BB, 3 players) A
SB bets 28.73 BB, Hero calls 28.73 BB, CO calls 28.73 BB

River: (130.27 BB, 3 players) 7
SB checks, Hero checks, CO bets 129.27 BB, fold, fold

CO is a big whale as you can see.
SB has been described to me as a fishreg but I don't have my own reads.

Should we just pile turn?
It seems like if we just gii ott in these kinds of spots with our continuing range that our range on rivers vs. SB (when CO folds turn) is immensely weak/exploitable and I thought this might be a nice hand to "defend" our turn calling range with.

I like calling turn, sure it's nice to deny equity from CO but you want him to continue with his dominated hands as well. You're right that calling here protects your weaker flop calling range that includes a lot of draws, can often buy you some cheap show downs when SB gives up sometimes and prevents you getting barrelled with a high frequency because you'll have some strong bluff catchers going into rivers. River looks completely fine considering the pot is 3 ways and you have really bad card removal (not blocking straights, blocking bricked diamonds etc.)

I really dislike calling turn tbh.If this was HU sure call is fine.But in a 3way pot no need for

defending your calling range and being balanced,not sure is that even possible.Against big

whale i don`t think call would be too bad,but generally would prefer folding here.

42/25 SB
56/16 CO

Balance, hmmm