The U.S. gives highest priority to family members of citizens and immigrants with work permits (which are often known as green cards) under the philosophy that immigrants with family members in the U.S. are more easily integrated into American society. Over two-thirds of all immigrants enter the U.S. through family reunification. Humanitarian protection and employment-based immigration account for the other third of legal immigration.
Canada's system, on the other hand, takes a different approach. Although it permits immigration through family reunification and humanitarian protection channels, it primarily relies on a point system to determine who will be permitted through economic channels.
The point system is designed to encourage immigration by those who seem likely to make the greatest contribution to the Canadian economy. The system awards points based on criteria such as level of education, languages spoken, occupation and whether or not the immigrant has relatives in Canada. Only candidates with enough points can apply for a Canadian work visa.
So at the outset, the two systems were set up for very different purposes -- and encourage very different types of immigration.