Most major Canadian cities are close to the US border, for three very important reasons: geography, temperature & economy. Geography: because a good part of the country is covered in Canadian Shield, making it very expensive to excavate land. Temperature: because the nicest temperatures are near the border. Economy: Transit to exporting is cheaper if you're near the border.
Why would Vancouver be around for Seattle? Wouldn't that be the other way around based on population? Also, if we're going to use US exceptionalism as the standard, then you should help explain Detroit vs. Windsor. Because Windsor isn't getting torn down neighbourhood by neighbourhood.