I am more inclined to support Nicaso's theory of a confederation of Montreal Italian crime groups which I think, will also include one or more Ndrangheta clan(s)and a weakened Sicilian clan among them. I can't see a single Mafia godfather scenario happening but I do see one emerging as a dominant group sharing power with others.
With regards to Rizzuto alliance with the HA. I find that alliance was deteriorating prior to Vito's arrest. The D'Amico feud was not handled well,I believe had Vito not been imprisoned, that feud would of been settled amicably. The D'Amico's being allies of HA did not help the relationship. Furthermore, Sergio Piccirilli (a childhood friend of Sal Cazzetta HA president) getting involved in the feud also did not help matters.
As the war progressed they tried appointing interim leaders to lead the mafia on a number of occasions but failed to rally the different factions. This failure was also illustrated by the number of meetings the Mafia, street gangs and HA had to have in order to settle disputes without success. It was posted in some articles that the HA were not pleased with the interim leaders of Stefano Sollecito and Leonardo Rizzuto.
I also believe that when Rizzuto came out of jail, even though HA relations were strained but not broken, Rizzuto still managed to revive an alliance with HA in Montreal and even met with the London ON, HA in the Republic Dominican. We do know that HA Mom Boucher & Leonardo Rizzuto conspired to murder of Raynad Desjardins. Up until this point HA was still in business with the Rizzuto clan.
With Rizzuto death and no one able to succeed him, it became more apparent for HA to back the rivals. It is sometime after the police raids of Nov. 2015 & arrests of Leonardo Rizzuto and others that I think the Ndrangheta may have made an alliance with HA but at this point it is just a theory.