Just in regards to the density figures ...
You need to be really careful what you are comparing.
As a simple example, Boston ... Boston proper is 4X smaller than Toronto (area wise) as it never went through amalgamation, yet the density is only slightly higher than all of Toronto ...
Also there are many different density figures that take into account things like green space / water.
Toronto as an entire city is actually fairly dense as far as cities go in North America.
Toronto's outer core, (i.e. right around downtown but not downtown it self) not so much ... this is because many cities, take Montreal, have short 3 / 4 story buildings surrounding the core, as opposed to TOronto's Victorian era houses.