Here are all the great lakes cities by population, with 'cities' defined as contiguous urban areas rather than MSA/CSA etc (the best definition IMO).
Chicago 9.14 million (includes Kenosha)
Toronto 6.53 million (includes Hamilton)
Detroit 3.73 million (excludes Windsor, Flint etc)
Cleveland 1.76 million
Milwaukee 1.40 million
Buffalo 0.930 million
Rochester 0.725 million
Toledo, OH 0.5 million
Windsor, ON 0.285 million
Erie, PA 0.195 million
Land area:
Chicago 2,647 sq miles
Toronto 888 sq miles
Detroit 1,335 sq miles
Cleveland 772 sq miles
Milwaukee 546 sq miles
Buffalo 380 sq miles
Rochester 325 sq miles
Toledo, OH 240 sq miles
Windsor, ON 68 sq miles
Erie, PA 82 sq miles
http://www.demographia.com/db-worldua.pdf