This turn against immigration is really the dumbest, most self-defeating thing Canada can be getting up to. You know why the US presents such a threat to us? Because they represent a productive capacity of around ~340 million people while we represent a productive capacity of ~40 million people. They managed that by having extremely lenient citizenship requirements (for whites, but we can adopt similar policy without the racism) for most of their history.
Pursuant to this power, Congress in 1790 passed the first naturalization law for the United States, the Naturalization Act of 1790. The law enabled those who had resided in the country for two years and had kept their current state of residence for a year to apply for citizenship. However, it restricted naturalization to "free white persons" of "good character". Oddly, the law authorized any "court of record" to perform naturalization. In other words, for over 110 years, any federal or state court of record could naturalize a qualified applicant.
https://en.wikipedia.org/wiki/History_of_immigration_and_nationality_law_in_the_United_States
Which, far from collapsing, turned it into the wealthiest and most productive country on Earth at the time.