Most of the large cities in Canada are located close to the US border. For example, there are Toronto, Montreal and Vancouver.
Most of Canada's population lives along the southern border because of the climate. Although Canada is very large geographically, a lot of the area is, not necessarily uninhabitable, but has much more extreme weather conditions (colder) and is more expensive to live in.
The earlier settlers settled closer to the south because of the water channels, especially the St. Lawrence river which flows out to the Atlantic. Early settlers travelled by boat, which transports only in bodies of water.
The Americans felt that it was their destiny to expand their territory. They didn't want any other countries to take land from them. They only wanted to protect their land.
