A tour that involves the Icefield Parkway in Canada. When I rode it (on pavement), I started in Missoula, MT and went into Glacier National Park and while I had planned an off-road, camping kind of trip, a major flooding event forced me to re-route and I ended up following the ACA Northern Parks route all the way up to Jasper. It took about a month and is one of the best trips I've taken. I wrote
a detailed journal of the ride, if you want to see some photos and learn more.
Another suggestion I have is Northern Italy. I'd include Slovenia and Switzerland, as well. You could fly into Ljubljana and head west to, say, Geneva or keep going into France. I've done various tours in these areas and none of them fail to impress.