While it's possible that any member of the Corleone family who had attended the meeting with Sollozzo and Bruno Tattalglia could have put his life in danger by doing so, the one likely exception would have been Sonny - whom Sollozzo needed to keep alive in order to recruit him as a potential future business partner in the narcotics trade.

By this point, the only member of the Coreleone family who definitely had a target on his back - in addition to Vito himself - was Luca Brasi, as liquidating Luca was the key to the success of Vito's assassination, which in turn was the key to the success of the entire new enterprise.

The fact that Vito selected Luca to go straight to Sollozzo was just a very convenient bit of serendipity from Sollozzo's standpoint. If Luca has not made it easy for them by walking right into their trap, they would have had to devise some other means by which to take him out.

~ Q