The border is a straight line!

Credit: The Center for Land Use Interpretation, United Divide: A Linear portrait of the USA/Canada Border. Chapter 3: The 45th Parallel.Source: https://clui.org/projects/united-divide/45th-parallel. All data on the CLUI site is subject to a Creative Commons Attribution-Noncommercial-Share Alike 3.0 license.
The boundary line brushes against the barn as shown by the white border marker and the cleared trench that stretches to the horizon.