I've always felt that five years should be the minimum number of years of residence before people are qualified to apply for citizenship. A five-year period seems to be, I would guess, the average of most other countries. Switzerland and Germany require eight years, and some countries, of course, don't allow people to apply for citizenship. The five-year period, I think, was in the original legislation, the Citizenship Act of 1947, and the idea was that immigrants coming to Canada would have to acquire domicile before they were eligible to apply for citizenship, and to acquire domicile meant they had to be legal residents for five years. After they had the five years domicile, they were then eligible to apply for citizenship.
On April 14th, 2016. See this statement in context.