D. Exfoliation is the answer
A large part of that land area is not conducive to farming or general use. The Canadian Shield covers about a third of the nation. The Arctic permafrost probably covers another third. You cannot farm in either of these areas and the cost of building roads and infrastructure in or through these areas is very high. Other areas have land that could be used for farming but the season is too short. On the lands that are arable, Canadians are reasonably densely populated.
<span>As to softened immigration process, the percentage of permanent residents (generally recent immigrants) has remained fairly steady at less than or at 1% of the population for at least 50 years. Since the birthrates for multi generational Canadians (Canadians whose grand parents or before were immigrants) is so low, Canada needs immigrants to maintain the population at a sustainable level. Yet the processes have not gotten easier. The most recent iteration of the Immigration act has extended the time required for a landed immigrant to live in Canada before being eligible for citizenship (from three years in five to four years in six).</span>
Competition, Social Hierarchy, and Territorial Imperative
When the rocks are exposed, erosion begins
