Not only that, but when filing out immigration petitions, most firms will actually file in Canada and the US. Workers who can't meet the higher bar for US immigration will be sent to Canada.
We don't have sufficient birth rates to maintain things and so both economic productivity but also the tax base will be significantly harmed without this immigration.
That's not to disagree with your comment, the large amounts of immigration do cause problems and as you say, much of it flows into certain cities.
With family reunification, it's not uncommon to see aging parents and relatives be sponsored. They add very little to the tax base but are a huge burden long term.
Also, there are some requirements to support those family members:
"You will also sign a Sponsorship Agreement, obligating you to financially support your sponsored relatives if they cant provide for their own needs. The new permanent resident will not qualify for government assistance, even after the sponsored person becomes a permanent resident, separates from you, or leaves the country."
"To sponsor a parent or grandparent, you must obligate yourself for 20 years of financial support."
https://greenlightcanada.com/how-much-does-it-cost-to-sponso...
Canada is facing a huge brain drain to the US, for highly paid and in demand professions like in healthcare and tech. It remains to be seen whether or not they can replace the lost productivity of their native expats with mass immigration.