[Rdd]

It’s a very interesting question though.

The main US networks are carried on cable in Canada, through stations near the border. However they are subject to Canada’s infamous simultaneous substitution rule, which basically says that if a local station is carrying the same episode of the same programme as an out of market station, the signal of the out of market station must be substituted by the cable provider for that of the local station for the duration. While the rule is written in broad enough terms it is squarely aimed at US stations and for the benefit of Canadian ones, and Canadian networks programme accordingly to maximise the benefit for themselves.

Presumably then, if no simultaneous substitution is in effect, the Canadian viewers of US stations would indeed see interruptions, but they might not if simultaneous substitution wasn’t in effect (although I would imagine the mere fact of the interruption would technically mean subsuming wasn’t required from that point).