Great Idea! In addition to the TAT, there's also:
Trans Canada Adventure Trail (TCAT): www.graveltravel.ca
Washington Backcountry Discovery Route (WABDR)
Oregon Backcountry Discovery Route (OBCDR)
I think there's also a continental divide route that goes from Canada to Mexico, crossing the continental divide at least a dozen times, though that may be motorcycle only.
There are probably others as well. If I REALLY had the time, I'd love to take TCAT across Canada, then TAT back to the west coast, then OBCDR and WABDR home. to complete a North American loop, but to do it properly, I'd want to take at least six months. Maybe when I retire...
We ran a portion of WABDR last summer, and I did part of section 2 (Durr Road from Yakima to Ellensburg WA) yesterday. This summer Wazuks is planning to do at least the northern half (north to south, from the Canadian border to either Wenatchee or Ellensburg.) Date will depend on snowpack, as portions are over 6000'. Last year we were turned back by snow the last weekend of June; hopefully this year won't be as bad!