Looking at Niagara, ON, CA, compared to Buffalo and Erie County, NY, USA, do you think the Niagara River impacted which country would have the major city that is in the top 50 of biggest cities in North America as the countries grew?

Eh, so Buffalo-Niagara-St Catharines is really just one large Metropolitan area with a population of 1.6 million. The biggest factor though is that there's no large cities on the Great Lakes other than Toronto in Canada. Canada doesn't have a Chicago, Detroit, Milwaukee or even a Cleveland. A lot of that simply has to do with climate. Unlike the US, that area isn't nearly as good for agriculture. Canada has the Welland Canal but this was much less important. Toronto really wouldn't explode in growth until the 1950s. There was no NYC type city to fuel the growth of Port Colbourne to the size of Buffalo. It's also kind of obsolete with canals connecting Lake Huron directly with Lake Ontario.