Originally Posted by
SEA1K4EVR
Note the flight SEA-YVR is on Air Canada, so it's not cabotage. It would not be possible if it were Skywest for both segments.
Though the OP's example isn't cabotage, the reasoning above is incorrect, as far as I'm aware.
It isn't cabotage because a US-based carrier has the ability to sell a ticket from a US destination to another US destination. They could connect in FRA for all anyone cares (though that's a long trip).
On the other hand, if it was Air Canada selling that route, it would be cabotage.