Well it's not really surprising that New York City's numbers are denser than Chicago's. New York has far far more highrises apartments, midrise apartments and dense rowhouses which are much denser forms of housing than detached houses which is the main housing type in Chicago.
Toronto is probably more like Chicago in terms of density in the city proper, although there are some differences. Like Chicago, Toronto had and to a lesser degree, still has lots of industrial areas. Most of the waterfront was taken up by a huge railyard that is now being redeveloped into new neighbourhoods like City Place and South Core:
http://urbantoronto.ca/news/2010/03/...lost-toronto-0
The areas East and West of the Financial District were also largely warehouses and manufacturing including areas like the Entertainment District, Fashion District, Liberty Village, Distrillery District, St Lawrence and King East. These areas are mostly being turned into lofts and condos right now, with a few non-residential uses too. There is also a huge area on the waterfront that was landfilled in the early 1900s and mostly consists of newer industrial buildings (many abandonned), vacant land and parking lots. There are also massive industrial areas around railway yards and airports further from downtown. The one around Pearson Airport which is mostly outside city limits is over 50 square miles of non-residential lands (there's also some office parks, hotels and big boxes).
Downtown Toronto has quite a lot of apartment buildings, both older rental buildings and newer condos, maybe more than in Chicago. The downtown area had about 120,000 residents in 2001, around 180,000 in 2011 and will probably have around 250,000 in 2016. Outside of downtown, the inner city is mostly attached, semi-detached and detached houses, although the basements and second floors are often rented out to separate households, which is more or less like Chicago. Most commercial streets that are pre-WWII are 2-3 storey with apartments above the ground floor.
Beyond that is a bungalow belt of sorts, although it's not quite like Chicago's. Much of Toronto's "bungalow belt" has 2-4 unit apartments and 2 storey houses (many of which are new) mixed in. The city proper also includes a ton of post-WWII areas. The earlier post-war areas are mostly bungalows on large lots while the newer areas from the 70s-90s are two storey and generally on smaller lots. There is also a substantial amount of highrises throughout the inner city and suburbs that help raise density somewhat, they were built in multiple waves with much of them built in the 60s and 70s as rentals, followed by a small wave of condos in the 80s and bigger wave of condos in the last 15 years. However, those built in the 60s-80s were surrounding by greenspace, parking lots and sometimes shopping malls, so the density is not as high as it could be.
Outside the city proper, the single family homes built in the 60s are mostly bungalows on large lots, followed by 2 storeys on relatively large lots in the 70s and 80s and 2 storeys on small lots in the 90s/00s. The 60s-80s areas have densities of around 5-10k ppsm while the newer areas are more around 10-15k ppsm. In NW Brampton, where a lot of the greenfield growth is occuring, you also have a lot of South Asians with extended families lead the average household sizes of 4-4.5.
As for the population of the old city (city limits pre-1998 amalgamation of several suburbs), it's gone up and down since WWII but for the last 30 years it's been increasing and is now at its highest.
I also gathered quite a lot of data on the density distribution of Canadian cities.