The Akwesasne Mohawk tribe that operates a small casino at the St. Regis Indian Reservation, straddling the New York State / Canadian border, has NEVER allowed border guards or a a customs installation, like at other national borders.
Anyone can walk from Canada into the U S A (and Vice Versa) without a concern. The Mohawks charge a cash fee to escort an interloper. In fact, this trafficking in ILLEGAL entry into the USA has been an ongoing business for generations. That enterprise, (along with wholesale marijuana operations) is documented in a prize-winning motion picture produced just a few years ago. I apologize for being unable to recall the title.
I spent a lot of time on that reservation, especially in the 1990's, and this is an "open secret" there. References to same is knowingly met with "a wink and a nod."