The Country that shares the southern Border with the US is Canada.
Two countries share a border with the United States. To the north, the US shares a border with Canada. To the south, the US shares a border with Mexico.
CanadaCanada shares the longest border with the US.
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The US
Canada and Mexico
Both Canada and Mexico border the US.
Mexico
Both the US state and the country border each other.
Mexico
Texas, New Mexico, Arizona, and California all share a border with Mexico, the only Spanish-speaking country that borders the US.
Mexico.