In the late 1970s or even the 80s the New York families weren't that much in decline yet and still very powerful. Their real decline started in the 90s. However, for the Bonannos the 90s were a good time and it wasn't until their entire administration flipped that everything fell apart. Montagna's status meant enough for people to align with him. However Desjardins himself didn't have much to do with the Bonannos at that point and neither did his guys which is why they didn't care for him to be the leader, and when Montagna tried to take out Desjardins it was simply kill or be killed.
You're correct, the American Mafia was still powerful in the 70s/80s but it was in a steady decline. The truth is the American LCN was at its highest peak from the 30s to the 50s, they ran the syndicate like an oiled machine and no other Italian Mob group around the world compared. Then you had significant turning points such as the Apalachin meeting and the Valachi testimony, both of these events were the beginning of the decline. American LE started to catch up and with each decade, their power and influence decreased.
The American Mafia as a whole was in decline by the 1970s, but the New York families weren't that much affected until the mid 80s. It wasn't until the 90s that they lost much of their power over the unions among other things. By that time the Bonannos weren't involved in the unions anymore and so were able to fly under the radar and left unscathed until the early 2000s.
During the 70s/80s the Montreal Mob was still very much so under the Bonnanos, by the 90s I would argue that they were under the Bonnano banner by name only but were independent and acted as such, they did kick up to them but I feel it was out of respect for Gerlando Sciascia since he was very close to Vito. Once Sciascia was gone, that was the end of it as it was clear that no more envelopes were being sent. Vitale was apparently sent to Montreal to make Vito a capo around 2001, he was received with respect and all but Vito declined the offer, that was a clear message to the Bonnanos that just in case they did not understand the memo back in 1999 (No more envelopes)
It hasn't been made clear whether envelops were still being send or not after 1999. Vitale even admitted as such. Domenick Cicale, another turncoat, claimed that tribute was still being send. He also said that Massino and Rizzuto partnered a stripclub. In addition, journalist Daniel Renaud stated that Montagna was used as a go-between and reguraly traveled to Montreal in the years before his deportation.
Anyway, this discussion seems to be never-ending due to conflicting statements, opinions and preferences. And even if Massino himself comes out of the woodwork and states that he was still receiving tribute, the people believing in the 1999 indepence will probably refute it.
As for myself, I don't think or very much doubt that the Bonannos are still involved in Montreal, but I don't believe it ended in 1999, unless Massino confirms it.
"It was between the brothers Kay -- I had nothing to do with it."