Sponsoring elderly parents to retire in the US seems prohibitively expensive in terms of healthcare cost. Maybe that's why Canada disallows it, since their healthcare is covered by taxpayers unlike US healthcare.
ACA/medicaid pays healthcare expenses for elderly parents in US - no problems here. Technically government can go after sponsor for first 5 years after immigration for medicaid money but there are no known cases of government actually doing it. If parents qualify for ACA (need to make 20k/year - can be childcare “payment” for grandkid) then it’s like $20/month and sponsor is not even on theoretical hook to repay.
ACA doesn't pay long term nursing home fees for e.g. bedridden parents though. That can easily cost a fortune.
But then what do you do, return to your home country when you parents need help? Abandon your new life and job, which you built over 20 years?