The data is from 2015, but you can also compare it to and show the change from 1990.
Here is the Greater Toronto and Hamilton region (16.8 million people reside in this screen grab):
Here is the New York City region (55.4 million people reside in this screen grab):
And here is China (1.054 billion people reside in this screen grab):
I tried to capture both Shanghai and Hong Kong in this image. Guangzhou, Hong Kong, and Shenzhen are currently in the mist of forming a 40 million-person megalopolis.
If we pan back over to the northeastern United States and Central Canada – keeping the same scale as the above image from China – it looks like this:
These last two images say a lot.