I think you should drive the extra hour west and cross at Ivy Lea (1000 Islands). This crossing takes you directly to interstate 81. If you cross in Cornwall, you would have to spend time on secondary roads before getting to the interstate.
We drive almost yearly and our preferred route is Brockville, Highway 401, I81, I77, I26, I95, I4, Orlando.
We stopped in Rock Hill S.C. last time after about 14 hours driving.
Cheers
John