As usual, I beat the drums for US14. You could take the trans-am or enjoy the tailwinds in the Colombia River gorge as far as Yellowstone, see the sights there then pick up US14. This will take you over the Big Horn Mts. (A fearsome climb, I'll admit), The Black Hills (Mt. Rushmore, etc.) and The Badlands.
Then cross Minnesota and Wisconsin to Manitowoc where you take the ferry to Ludington, MI. Bike across Michigan and into Ontario at Port Huron, across southern Ontario to Buffalo , NY. There you could pick up New York bike route 5 or do the Erie Canal Trail.
However, if you do the Northern Tier You have the advantage of being able to jog north and take in Jasper and Banff Parks, arguably the most spectacular scenery on earth.
If you do either one of these, don't forget your passport.