In a move that had to happen in order to create a literal North American Union, the U.S. and Canada have essentially agreed to allow the other’s army to cross the border during non-military emergencies:
In a ceremony that received virtually no attention in the American media, the United States and Canada signed a military agreement Feb. 14 allowing the armed forces from one nation to support the armed forces of the other nation during a domestic civil emergency, even one that does not involve a cross-border crisis.
The agreement, defined as a Civil Assistance Plan, was not submitted to Congress for approval, nor did Congress pass any law or treaty specifically authorizing this military agreement to combine the operations of the armed forces of the United States and Canada in the event of a wide range of domestic civil disturbances ranging from violent storms, to health epidemics, to civil riots or terrorist attacks.
Besides heralding the inevitable merger of the U.S., Canada, and Mexico, this could be a way the U.S. government gets around the pesky Posse Comitatus Act, which prevents the use of soldiers as policemen. If the soldiers are Canadian, one assumes that Posse Comitatus doesn’t apply.
Sharing air defenses through NORAD is one thing. Deploying Canadian troops to, say, keep the peace if the Detroit Pistons win the NBA championship is something else again.