It appears that the people who outright reject multiculturalism and the population growth that is largely a result of it, as Ibbitson points out, either don't understand the economic necessity of increasing the population, or choose to ignore the facts. First of all, a small population does not in any way mean that people will be more prosperous or that the economy will be stronger. In fact the opposite is true.  The United States with ten times the Canadian population has the strongest economy in the world, so that theory is easily debunked. 
Secondly, Canadians no longer have large families by choice. Fifty years ago, it was not unusual for couples to have between eight and fourteen children, especially in Quebec. But as women became educated and chose to enter the workforce, they no longer wanted large families. So immigration is the only way to increase the population. 
And increase it, we must to retain the taxpayers' base necessary to sustain the social programs Canadians want.