I speculated a while back that Sol may have approached Barzini first about a drugs deal because he figured Barzini had the most to gain from partnership with him, while Vito, already on top with rackets far less dangerous than drugs, didn't need Sol. I also speculated that Barzini advised Sol to go to Tattaglia because Vito wouldn't be worried about him, but would be concerned if he knew that Barzini was Sol's partner. Just speculation.

No, Tom didn't suss out Barzini. But, what surprises me is that Vito didn't figure that out, either. He said to Tom after the Commission meeting that he didn't know until that day that Barzini was behind it. "Tattaglia is a pimp--he could never have outfought Santino" Well, Vito, Tattaglia was a pimp before the Great War of 1946--how come it took you that long to figure it out?