"but what if the massive influx of immigrants, with the attendant pressure on housing and increased competition for jobs (resulting in downward pressure on wages), is making it more difficult for Canada's native-born population to establish families and have children?"

IMO this should be points 1, 2 and 3.  There are REASONS why our native population base is not having kids and enhancing immigration is merely a short term band-aid that makes the underlying problems worse.  drive down wages, make resources more scarce AND harder to access... Immigration is a self-fulfilling prophecy thanks to government mismanagement.