Cabotage describes a series of laws and rules which are specific to a given nation. The fact that US law might prohibit AC from selling a ticket NYC-YYZ-LAX does not mean that another country prohibits the sale of a parallel routing in its geography. So, forget comparisons to the US, Canada, and other countries.
OP's question is solely a matter of local law and that is where he needs to look. If there is expertise on that specific issue here, it may help to know what that is. Otherwise, the fact that what OP proposes could not be ticketed between two points in the US is not informative.