Vito foresaw the betrayal because of his cunning and because he had been doing "business" for so long. The Corleones were seen as weak, fleeing New york, and presumably falling apart at the seams. Everyone underestimated Michael...well almost.
Going through the list:
Neri -- No way. He was Michael's man. It was Michael who brought him in and brought him close. It has been said Neri was Michael's Lucca Brasi. He had gone from nowhere to being at Michael's side. Also unlike most of the others he did not underestimate Michael.
Rocco - Made his bones by killing Paulie, and with Michael ascending, Rocco was broen off from Clemenza to form his own secret regime. Barzini could not touch him.
Carlo had already betrayed the family to Barzini. Once that was done Barzini had little use for Carlo. He was a witless traitor.
Fredo - Still more or less loyal, and pretty much out of things in Vegas, there was no way Fredo would have the credibility to tell Michael he was in a position to make a deal and guarantee Michael's safety.
Tom - Tom was the ultimate insider, even when he was "out." He intuited there would be a betrayal, and he intuited there was a secret regime. He did not underestimate Michael.
Tessio and Clemenza - The most likely suspects. They had muscle, they had influence and they could be approached by Barzini who promised them they could keep their territories, run their family and not go down in flames with the collapsing Corleone family, if only they would betray Michael. In the end Clemenza remained loyal, and Tessio approached Barzini. We know this because at the funeral when Tom guessed wrong and thought it was Clemenza, Michael said that Tessio was always the smarter of the two, and it was the "smart move." This tells us Tessio went to Barzini.