Those immigrants are flooding into North America to compensate for low birth rates in Canada and the USA. They are flooding in to work nasty jobs (e.g. cleaning, picking berries, construction laborer, etc.) that native-born North Americans are unwilling to do.
The difference between Canadian immigration policy and American immigration policy is that Canada openly and honestly welcomes a half million skilled immigrants per year, favoring those of working age with a decent income. Immigrants earn points by completing university, earning professional credentials, speaking both of Canada's official languages, etc. Ironically, immigrants are far more likely to be bi-lingual or tri-lingual than native-born Canadians. The only problem is that their other language is likely to be Africaans, Arabic, Aramaic, Bulgarian, Cantonese, Croatian, Dutch, Farsi, Finnish, German, Greek, Hindi, Hungarian, Indonesian, Japanese, Korean, Kurdish, Mandarin, Nigerian (another dozen languages), Polish, Portugese, Punjabi, Russian, Serbian, Spanish, Tagalo, Ukrainian, Xhosa, Zulu, etc. ... and those are just the immigrants that I work with every day ...
Over their working lifetimes. those skilled nurses, dentists, doctors, engineers, etc. will repay the federal gov't (Ottawa) with income taxes that exceed their re-settlement costs.
OTOH The USA treats immigrants like criminals. By allowing the great unwashed masses ... your poor, your tired ... the USA is importing only low-wage-earners who become little more than a slave class.
Exploiting poor immigrants is not a uniquely American problem. See the book "Rat People" about poorly-documented day laborers living in cellars of major cities in mainland China. Most of these "rat people" came from poor farming towns in the interior of China who moved to the big city in search of work or higher wages. Corrupt landlords rip them off at every opportunity ... even if they are only forced to pay high rents for un-healthy cellar apartments. They are too poor to get state=sponsored medical care or educations.
How does this differ from the way the Charles Dickens' London was bursting at the seams a couple of centuries ago. See "A Christmas Carol."