Canada–United States border

There are two international borders between Canada and the United States: Canada's border with the northern tier of the contiguous United States to its south (6,416 kilometres or 3,987 miles), and with the U.S. state of Alaska to its northwest (2,475 kilometres or 1,538 miles). The section between Canada and the contiguous United States is the second-longest continuous international border in the world after the Kazakhstan–Russia border, and the two sections together form the longest border by total length.

Source: Wikipedia — Canada–United States border (CC BY-SA 4.0)