I can only speak for North America, and I don't have estimates of regional population data easily at hand. But speaking in broad strokes:
Agricultural
Eastern Woodlands (Roughly all of North America east of the Missississippi River and south of of sourthern Canada)
The Southwest (Modern Arizona, New Mexico, Colorado, Northern Mexico, etc.)
Hunter Gatherers
Pacific Northwest (Modern British Columbia, Washington State, etc)
Central Plains (Central Texas all the way North through Montana, the Dakotas, Alberta, Manitoba, etc.)
The Arctic (Northern Alaska in the West all the way east to Greenland)
Regions I haven't studied enough to have a good answer for
The Great Basin (Nevada, Utah, etc.)
California
The Canadian sub-arctic.
From the human ecology school of throught, it comes down to environment. If a group has ample access to water, they are more likely to be agriculturalists. That's why you see farming in the east, but not on the arid plains. The Southwest cultures had sophisticated irrigation systems to allow farming in the desert. The extremely wet Pacific northwest was abundant enough in resources that cultures never had to switch to farming to support their population, which is unusual for North America. The Arctic was simply to cold for the maize farming much of the continent had adopted by 600 BP.
SOURCE:
Various volumes of Handbook of North American Indians that I've looked at throughout my academic career. They are all nicely sorted by culture area.