Originally Posted by softee
Correct. Since Toronto, Hamilton and Oshawa are all separate CMAs, Statcan counts their urban areas separately from one another even thought they have long since grown into each other and formed one contiguous urban area.
Demographia has rightly combined them into a single urban area.
The closest US equivalent to CMA is the MSA, Metropolitan Statistical Area. Since MSAs are based on upper tier municipal boundaries, Oshawa and Burlington would be part of Toronto MSA, but not Hamilton. MSA requires 25% of residents in one municipality working in another municipalities, and only 24% Hamilton residents work in Toronto. So Hamilton would be its own MSA, and thus it would be its own urban area, even by US standards.
US also has CSAs, combined statistical area, which are combinations of MSAs and micropolitan statistical areas, and has 15% requirement instead of 25%. This would mean a Toronto-Hamilton-Guelph-Barrie CSA. But they would still be considered four MSAs, at least four urban areas, not a single urban area.