I don't think you can upload the maps...just tracks, routes and waypoints.Check out this site US Trail Maps
These maps are accurate up to a few meters and are up to date.
I just got off the phone with them, (supper nice guy) they will have much more to offer before the trails open. More states and update on current maps in a few weeks.
Each map has all state and local trails mapped along with pit stops/gas etc.
These maps are made to be uploaded to your GPS.
This is what many of us have been waiting for!!!