Stacks: Villain (BU) w/ 6400; Hero (BB) w/5500; Villain 2 (MP) w/ 6000.
Blinds: 100/200
MP Limps, BU limps, BB checks.
Flop comes 5 6 9 no FD.
BB checks, MP bets 200. BU raises to 600, BB calls, MP calls.
Turn 9 bringing a FD.
BB checks, MP checks, BU continues for 1600, BB calls, MP calls.
River is an offsuit 3.
BB checks, MP checks, BU checks. BU shows A9o, Hero wins with 96.

My question is how should I play this river to get the whole stack. My thinking was that it looks crazy strong if I just lead the river huge into 2 players, having just been flatting flop and turn. BU is repping pretty strong hands like 78, 55, 66, and I'm sure those would bet river. I decided check raising the river was the best way to get stacks in. Obviously, if I knew BU raises flop with top top then I would just raise turn when I boat up. Anyway, would love to hear thoughts about how to play this river with the nuts.

7300 in the pot and you have 3100 behind. you are first to act and there are 2 more behind and you have the nuts (87s straight flush possible?)…. don't wait for a Fancy check raise, just shove or bet big for value.

after the Action OTF and OTT at least 1 or Maybe both are going to call you

Betting your hand would be a good start.

To be honest, I'm not exactly sure about the stack sizes. I know the bet sizes are correct, and the blinds are correct. I know that I was the shortest of the 3 stacks. I agree with you guys though, I should've just led out.