I don't know the situation well as I don't live in Canada, but from all the discussions on different forums the picture may be like this:

Joe Di Maulo conspired with his brother-in-law Raynald Desjardins and the former Bonanno boss Salvatore Montagna to take over the Rizzuto clan. So they killed Nick and some of his underlings while Vito was in prison. Later, they had a conflict within their own group and Desjardins had Montagna killed with either Di Maulo's or the Bonanno's permission (maybe both of them). Once Vito got out, he had Di Maulo killed and now is on top again. He also took revenge on Desjardins who is now in prison by killing his right-hand man Gaetan Gosselin.

As for Desjardins, he has a position in the mafia because his sister is Joe Di Maulo's wife. He is also rumored to be a made member even though not Italian, even though I don't know how true it is.

If I got something wrong, please correct me.