A proposed bill currently on the table in the United States would give the US President the authority to seize control of the internet in the event of a cyber-security emergency. (What is the definition of a cyber-security emergency?)
While the US President's authority would be limited to the internet infrastructure in the USA, much of the Canadian and even world's internet infrastructure is routed through or based in the US networks and American companies. The President would be able to direct which internet companies are on-line, off-line, restricted, who they can provide service to or cut off, etc.
An interesting story to follow over the coming months...