Apparently they have also practised a nuclear EMP attack using a short-range missile launched off a freighter. Such an attack could be conducted anonymously to escape U.S. retaliation. Furthermore, to deter the United States with the hope of avoiding the full-scale U.S. response that you described, a state may undertake a demonstration attack on Canada.
Is Canada prepared to defend its citizens and take care of any aftermath should it happen inadvertently, if not on purpose?