Original: Some of the most well-known cities of Southern Ontario are Barrie, Guelph, Hamilton, Kingston, Kitchener, London, St. Catharines-Niagara, Waterloo, and Windsor, and largest among them, Toronto and Ottawa (also part of the sub-region of Eastern Ontario).
Simplified: Some cities in Southern Ontario are Toronto, Ottawa, Barrie, Guelph, Hamilton, Kingston, Kitchener, London, St. Catharines-Niagara, Waterloo, and Windsor.