In 1794, the United States and Great Britain negotiated the Jay Treaty, established in part to mitigate the effects of the recently established boundary line between Canada and the United States on the native peoples who suddenly found their lands bisected. The rights and benefits originally set out by the Jay Treaty are now codified in statute, and continue to bestow upon Canadians with a 50% native bloodline (euphemistically referred to as “American Indians born in Canada” in U.S. immigration law) the right to freely pass the border and remain in the United States for any purpose, virtually unrestricted by the Immigration and Nationality Act.
Boos, Greg and McLawsen, Greg, "American Indians Born in Canada and the Right of Free Access to the United States" (2013). Border Policy Research Institute Publications. 69.