Nipissing Line

Okay so I read that during the negotiations leading up to the treaty of Paris the US had the choice between one of 4 options regarding its western border. One of these options was that the US give up trans-appalachia for an extension of New Yorks northern border across OTL Ontario to Lake Huron. This sceme was unacceptable to the southern states.

So WI Sullivan siezes Fort Niagara in 1779 and Clark siezes Detroit shortly thereafter? Leaving the US in control of the old north west would it still be possible to also attain the Nippissing Line?
 
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