How much time do you have? You say it's 1400 miles by the major roads, but my guess it will be at least 2000 via roads you'd actually want to ride on. The more time you have, the longer you can make your route, and the more flexibility you'll have. If you have time for 2500 miles, that'd be great.
Many state highway departments produce maps listing traffic volumes and shoulder widths for the state roads. They may or may not refer to these as state bicycle maps. Check the DOT websites for the states on the route. My most important critera would be to find low traffic volume roads, the lowest you can find. Google satellite views are another valuable (but time-consuming) tool.
Different people have different preferences, but my experience is that riding on high-traffic roads takes all the joy out of touring.
I second the suggestion to try to piece this together by joining various ACA routes.