No matter if you like Harleys or not, their website has a neat feature for planning a road trip.
http://rideplanner.harley-davidson.com/en/RidePlannerMain.jspIf your destination includes leaving the United States, it doesn't allow you to pick a non-US destination, but you can alter routes to leave the border. I didn't try it for Mexico, but I didn't have any troubles getting it to go as far north as Calgary, Alberta.