It is much closer to Mexico
Canada .
Mexico by about 700 miles
I believe it is Mexico
Mexico is warmer as it is much closer to the equator than Canada.
Denver is about 14 hours away from Canada and 9 from Mexico (driving)
In geographic terms, bot are equally close, bordering the United States. If you mean on either cultural or socio-demographic terms, it is much closer to Canada.
Ohio is closer to Maine than Illinois.
With 2.16 million square kilometers (0.86 million sq mi) from Greenland vs. 1.96 million square kilometers (0.76 million sq mi) from Mexico, Greenland is approximately 10% bigger than Mexico.
The U.S. (both countries have a common border).
South Dakota is closer to Canada than a lot of places are, but it doesn't border Canada. There are many US states that border Canada, so they are clearly closer to it than South Dakota, which doesn't. South Dakota is, however, closer to Canada than Florida is, for instance. South Dakota is also closer to Canada than it is to Mexico or England or South Africa. I'm not certain the intent of this question, but you might wish to clarify so that someone can answer more specifically what you need to know.
Canada and Mexico both border the US. The Caribbean countries as well as the Central American ones are also fairly close.