Wasn't this also some part of a UN land use plan. I used to have a map of this UN plan for the US and this area was shaded. I think the plan had biodiversity corridors, animal preserves and areas for human activity.
I believe you are right. The maps at the EPA website used to be interactive by "sister city", recapping the various projects, territories, dual agencies, etc., along the entire border. In that set of maps, there were various 'views' for such projects as I remember it. I did not see the interactive map links when I verified the archive webaddress the other day. They seem to be gone, but then I didn't dig deep into all the links either. So.. perhaps you can find more specific to the UN use plan, but yes, I remember something about that.
If you find it, post it please, and give me a ping... I'll do the same..