I have been looking at the lawsuits in the US that relate to something like this. Obviously, it is two different laws between the US and Canada. The US is pretty strict that a court cannot intervene in a religious decision, it is called ecclesiastical abstention, it was created by the Supreme Court in the 1970s. A civil court can hear cases that enter into the secular part of a religion such as property or injury to person, but they cannot delve into if a church has made the right decision in selecting a priest or it's internal structure of who is a member. Even int he Abrams v Watchtower decision the trial court judge wrote that even if the elders knew that the accusations were false that it is an internal matter and a secular court has no business dealing with it.
Though there is one US court that broke from the pack a little bit. In Pennsylvania their Supreme Court in Bear v Reformed Mennonite Church the court did rule:
"‘. . . (T)he Court has rejected challenges under the Free Exercise Clause to governmental regulation of certain overt acts prompted by religious beliefs or principles, for ‘even when the action is in accord with one's religious convictions, (it) is not totally free from legislative restrictions.’ Braunfeld v. Brown, 366 U.S. 599, 603, 81 S.Ct. 1144, 6 L.Ed.2d 563. The conduct or actions so regulated have invariably posed some substantial threat to public safety, peace or order.'"
"the “shunning” practice of appellee church and the conduct of the individuals may be an excessive interference within areas of “paramount state concern,” i.e. the maintenance of marriage and family relationship, alienation of affection, and the tortious interference with a business relationship...."
Though Mennonite shunning does go further. It prevents communication of anyone even within the home with the person that has been excommunicated.