Killing Montagna severed ties between the Bonnano's and Montreal. Montagna was a crucial link to rebuild that bridge and somewhat take over Montreal for the Bonnanos. Obviously times have changed and Canadian mobsters couldn't care less about some guy from NYC trying to run things.
This ain't the 50s
You're right, but being there in the first place was a mistake on their part. The New York families have enough problems in New York, let alone getting involved in another country.
As far as Canada deferring to the New York families? Well, the commission hasn't been in place in quite some time. If it were, then Montreal would probably have to defer to New York somewhat. But like you said, this ain't the '50s.
"I got news for you. If it wasn't for the toilet, there would be no books." --- George Costanza.
