Starting from 1765 to present day, how can the United States come to include Canada and Northern Mexico? You may leave Quebec an independent country if need be, however the rest of Canada and Northern Mexico must be included. I'm not too familiar with Canadian history, but I figure it would be easy to include Northern Mexico following the Mexican-American War if President James Polk had gotten his way in the treaty of Treaty of Guadalupe Hidalgo. Assuming Quebec is apart of this larger United States, the US would encompass an area of 20,875,046 km2 and today assuming population densities coincide with present day, a population of roughly 386,736,619 people.
Furthermore, what would be the political, military and economical implications of this super sized United States of America? For one, the US obviously wouldn't have Canada to rely on, which would in turn force the US to seek out stronger alliances elsewhere. I also doubt the US and Mexico would have good relations today.
By the way for anyone who cares, this US fits in with my alternate world I'm building which includes a larger and surviving Imperial State of Iran.