Nearly 90% of Canada's population lives...A. in the province of Quebec.
B. beside the St. Lawrence waterway.
C. along the west coast of British Columbia.
D. within 100 miles of the border of the United States.

D. within 100 miles of the border of the United States.

The geographical distributions of Canda correspond to the important regions formed by Ontario, Quebec, British Columbia, Alberta among the principals.

The reason for this is the important cities like Montreal, Toronto, etc, that have the most favorable climatic conditions present in the initial settlements when Canada was then colonized by the French once a time.

Together with the favorable climate, comes the economy that flourished as trade with the northern US states, initially trade became important in the region and nowadays much other cooperation and relations among neighboring cities has become the reasons for the significant shift in Canada demographics.

The northern states of Canada present the lowest population and in general the territories present harsh and tough conditions for the development of large cities (desertic lands in a permanent snow or tundra) .Since the ground is unfit for traditional settlement and construction, the lowest temperatures are recorded there and so people are unwilling to habit. There are some small settlements key for exploration of natural resources like oil in the north pole and artic islands.

In the following image the yellow represents the lowest demographic distributions as you can see the population concentrates just in the 100 miles border.