Wikipedia has Toronto at 10,750/sq mi, Chicago at 11,868/sq mi. I'm sure those numbers fluctuate often from source to source though.
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1. 9 DeKalb Ave - Brooklyn, NYC - SHoP Architects - Photo
2. American Radiator Building - New York City - Hood, Godley, and Fouilhoux - Photo
3. One Chicago Square - Chicago - HPA and Goettsch Partners - Photo
4. Chicago Board of Trade - Chicago - Holabird & Root - Photo
5. Cathedral of Learning - Pittsburgh - Charles Klauder - Photo
Toronto and Chicago..Who cares which is denser blah blah.. Both are classic examples of North American alpha cities overlooking the Great Lakes.
And ya, Toronto and Chicago kinda roll the same way..Both are lake front financial centres etc...Same MO..Toronto is very much Chicagoesque it seems.