Which country borders the United States to the north?

Canada borders the United States to the north. It shares the longest international land border in the world, stretching over 5,525 miles. This border extends from the Atlantic Ocean in the east to the Pacific Ocean in the west and includes various landscapes, such as mountains, lakes, and forests.

For additional context, Mexico borders the United States to the south, while Russia and China are not contiguous neighbors but are located across significant bodies of water (the Bering Strait in the case of Russia and the Pacific Ocean for China). Thus, Canada is the only country that directly shares a land border with the United States to the north, making it the correct answer.