11-Jun-2014 -- After spending an enjoyable day in Waterton Lakes National Park, Alberta (even though I failed to reach its confluence point - [49,-114]), I reentered the U.S. at the entry point formed by the twin towns of Coutts (Alberta), and Sweet Grass (Montana).
This confluence point, which lies barely on the Canadian side of the border, could be reached from either town, but it is most easily reached from Sweet Grass, because a local road - Cemetary Road - runs westward, just south of the border, ending up just 500 feet from the confluence point. (A word of warning, however: The damp clay soil on Cemetary Road caused my 4-wheel-drive vehicle to slide around quite a lot. If you're in a 2-wheel-drive vehicle, then be wary of driving on this road in anything other than dry conditions.)
The confluence point lies at the bottom of a small hill, on slightly marshy ground, just east of a large pond. I had to battle a lot of mosquitoes as I walked to/from the point.