Why not do one of the multitude of fantastic long trails in the USA instead? Walking the southern tier sounds like an absolute nightmare. There's the PCT, CDT, AT, Hayduke Trail, or if you're looking for something flat and long you could try and do the North Country Trail. 

This country has so much beautiful nature, it just seems insane to walk several thousand miles on pavement when you could do some of the best hiking in the whole world instead.

But that's just me, I personally hate touring pavement in the USA because the roads are too high speed limit, the towns are mostly cookie cutter strip mall chain store bullshit, and why spend time on pavement when you've got the best long distance gravel options in the world like the GDMBR, Oregon Timber Trail, Plateau Passage, etc.