There's a number of irregularities between the US and Canadian border.
Johnny Harris, who used to (still is? seems unclear) film the Vox series "Borders", did a video on it:
https://www.youtube.com/watch?v=Vvvicd07zCs
Basically, the border is largely the 49th parallel and some seemingly arbitrary lines on the East Coast and Alaska. But since they were done in the 18th/19th century without regard for existing settlements, it leads to some crazy enclaves and border towns:
-Point Roberts, WA [1]
-Piney Pinecreek Border Airport (K48Y) [2]
-Hyder, AK [3]
-Estcourt Station, ME [4]
-Derby Line, VT [5]
[1]: https://en.wikipedia.org/wiki/Point_Roberts,_Washington
[2]: https://en.wikipedia.org/wiki/Piney_Pinecreek_Border_Airport
[3]: https://en.wikipedia.org/wiki/Hyder,_Alaska
[4]: https://en.wikipedia.org/wiki/Estcourt_Station,_Maine
[5]: https://en.wikipedia.org/wiki/Derby_Line,_Vermont