It's all laid out in the book Mafia Inc.

I can't recall this word for word, but I'll try: Sal Vitale visited Montreal in 1999, after the death of Gerlando Sciascia, with Anthony Urso; if you read about this meeting the truth is better than fiction.

In a nutshell: Vitale was there to "deliver the news" to Rizzuto that Sciascia had been murdered and to assure him that that Bonannos were looking for the real killers. Vito, already certain that Sciascia was killed by the Bonanno family, had chairs set out for himself, Vitale, Urso, Frank Arcadi, Paolo Renda and one other which he deliberately left empty, intended to symbolize a chair for Sciascia.

Vitale's real purpose fo the visit was to take a headcount, on orders from Massino, to assess how many "Bonannos" were in Canada. Vito Rizzuto responded that there were a total of 19 made members in Montreal.

Vitale then asked who was in charge to which Rizzuto replied that everyone in Montreal was equal and that no one was in charge. Vitale told Rizzuto he was authorized by Massino to offer him the Capo position for Montreal to which Vito politely declined; which was taken (perhaps as intended) as a direct insult to Massino.

The RCMP and FBI believe that it was at this point, following the death of Sciascia, that any tributes that were being paid from Montreal to NYC stopped. This was the point at which the Rizzutos formally, if without saying so outright, severed their ties with the Bonannos.

I would tend to believe that accounting of events, particularly given the lack of co-operating evidence any of Massino, Vitale, Cantarella, Coppa, Lino or others had to offer against the Montreal members, with the obvious exception of the events in 1981. None appeared to be in possession of any more recent knowledge.

Mafia Inc. is a great read, and the superior book to "The Sixth Family" - for a thorough understanding of the Rizzuto clan I highly recommend it.