Adjusting GPA between schools is one approach to deal with grade inflation between schools. SAT is just another approach with its own tradeoffs. I've simply listed why I prefer the former over the latter approach.
Canada's population is smaller but we also have many obscure rural schools. Non-prestigious universities don't have much data but they also don't have much choice in top applicants so it doesn't really matter. Over time, they can build up decently accurate profiles of high schools for majority of applicants.
They do a regression that includes both GPA and SAT. That is mathematically an adjustment of grades, where the adjustment is the SAT term. Then, as articles such as this one show, this correction correlates well with success at the university. So ultimately it becomes the same correction you want.
It would be interesting to see a study that compares SAT scores vs alumni performance to see which one has a better correlation with success to use for said adjustment
Canada's population is smaller but we also have many obscure rural schools. Non-prestigious universities don't have much data but they also don't have much choice in top applicants so it doesn't really matter. Over time, they can build up decently accurate profiles of high schools for majority of applicants.