I don’t recommend not filling it out because it’s the law and your duty as a Canadian citizen!
From the Vancouver Sun:
Q: What happens if I don’t complete the census?
A: People who are out of the country on May 10 will not be captured by the census. Those who have not submitted by the end of May or early June may get a home visit from a properly-identified enumerator, who can provide a survey and help people complete it. Statistics Canada also provides a help line with service in many languages. In 2011, the census had a completion rate of 98 per cent.
Those who refuse to complete the census could face a fine of up to $500 or up to three months in jail. Such refusals, however, are rare — in 2011 there were between 60 and 70 — and Statistics Canada refers such cases to the courts. Most of the time, judges simply issue a court order requiring the person to complete the census, though in 2011 there were a handful of fines.