What two countries border the most populous nation in the western hemisphere?

The Earth is divided into four hemispheres namely; Northern, Southern, Eastern and Western. The imaginary horizontal line at the center that divides the earth into the Northern and Southern Hemispheres is called the equator. All of North and South America which includes the Caribbean and Central America as well as Greenland and about half of Antarctica and is what Western Hemisphere is composed of. Mexico and Canada are the two countries in this hemisphere that border the most populous nation.