So many options and you have identified many, but costly options. Someone recently posted a route from Montreal to NYC:
Western New England Greenway | Bike Route | CT MA VT
If you are in DC, you can fly one-way to Montreal for <$150 + bike flying cost, then ride back as far as you than take train or flight back to DC.
Calgary to Banff to Jasper along Bow Valley and Icefields Parkway also nice. Many camping options along the way (and you can ask to share a space if camps are full). Use Brewsters bus service to ride back to Calgary from Banff, Jasper, etc.