Why are residents of northern Canada bombarded by more intense radiation than residents of Mexico?

Answer 1

Not necessarily. The northern lights are due to charged particles from the sun in the upper atmosphere guided to northern latitudes by the earth's magnetic field. They do not reach the ground. Much more energetic cosmic rays are the main source of ionizing radiation that people are exposed to from space. They are attenuated by that atmosphere, so dose increases with altitude, not latitude.

Answer 2

Well, that sucks.