I think assuming the war in Montreal is just a simple breakdown of Sicilians vs Calabrians is naive, but I don't think it's too far off. Some educated guessing here:

* The Rizzuto/C.untrera-Caruana takeover of Montreal was backed by more powerful groups in Sicily than we realize (not just their families in Agrigento). Possibly they were backed by Toto Riina and the Corleonesi in order to have strong allies in North America outside of the Gambinos.

* The Rizzutos still kept an alliance with the Bonannos for a very long time until George from Canada was killed which seemed to have damaged the relationship beyond repair, though they still work together at a smaller level

* The Corleonesi war against the Italian state and against the Palermo group led to a huge crackdown against LCN and also killed off generations of talent... it wiped out a lot of strength from their bench so to speak, making the Sicilian Mafia much weaker overall.

* The Calabrian 'Ndràngheta quietly stayed under the radar and avoided headlines, building their own connections for drugs in Latin America and setting up bases all over Europe, Canada, and with mobsters in the US.

* Vito Rizzuto did an excellent job keeping all of the different factions in Montreal relatively happy and at peace, but when he went away to prison it created a huge power vacuum. It seems like Project Colisee really hurt the power of the Rizzuto group and the people left out on the street who were trying to run the family were simply not respected and/or feared enough to keep all of the different factions from going to war. That’s when we see old vendettas and beef start to bubble up and leads to the current war that’s lasted since about 2009.

* Around this same time we see Cali and the Gambinos trying to re-establish their historically strong ties to the Palermo faction in Sicily. The Gambinos are also rumored to have connections to different 'Ndràngheta groups, likely in Ontario. It wouldn't surprise me either to find more evidence in the future of the Sicilian Mafia and the Calabrians working together.

* With the 'Ndràngheta taking control of the drug trade in Europe and the Gambinos wanting to re-establish control in Sicily, they possibly decide to fill the leadership vacuum in Montreal and form an alliance to push out Rizzuto. It's possible the Sicilian faction of the Bonannos were involved too and wanted to re-establish strong ties with Montreal. Which is why Montagna backed a faction trying to oust the Rizzutos even though Sal himself is Sicilian. Sal was probably too hotheaded and not diplomatic enough to pull everything off, but I wouldnt be surprised if he was somehow trying to reestablish both the Bonannos connections in Montreal as well as connections with the Gambinos in both Canada and NY.

* The Violis in Hamilton seem aligned with the 'Ndràngheta as well. They may have been made into the "Todaro Family" of Buffalo way back when it existed, but (guessing here) I don't believe it's still a thing now in spite of the recent reports from law enforcement. I believe they were made into Buffalo decades ago but Buffalo as a traditional LCN structure doesn't exist: The people left are loyal elsewhere (Hamilton? Calabria?). They're more like a drug network than an American LCN family.

Long story short, the Bonannos realized they made a mistake backing the Rizzuto faction, the Gambinos wanted to re-establish connections in Sicily, the Palermo faction is trying to regain control of what they lost in Sicily, the Violis wanted revenge, and the Calabrians being the dominant worldwide mafia group all helped push out the Rizzutos. There’s probably a strong network of Calabrians between Ontario, Montreal, Hamilton, Buffalo, and NY with the Gambino (& maybe the Bonannos). The reason we're hearing about made "Bonannos" in Canada is because the Rizzuto group is out of power and the Bonannos are re-establishing their presence.

But, here's the thing, I dont think they've been completely successful and obviously, some of the Rizzuto group is still in power. Montreal may split up now with no one group in total control... with no rats it's hard to tell. The reality is probably a lot more complicated and not as clean cut and neat as we think it is.