It is interesting how different this is from the CMA population estimates:
http://www40.statcan.ca/l01/cst01/demo05a-eng.htm
As many people have said, these figures are not very accurate because not all forms are submitted. Last census the numbers were corrected upward by about 3% on average. I don't know how much the return rates varied by city.
What is odd is that some census figures are approximately the same as the estimates, while others are far below:
City / 2010 est. population / 2011 census count
St. John's 192.3 / 196,966
Halifax 403.2 / 390,328
Calgary 1,242.6 / 1,214,839
Could the return rates vary that much between cities? Another possibility is that growth rates from 2010-2011 were dramatically different from 2007-2010, but that seems unlikely. I wonder what else could explain the differences?