It's the law.
One in four randomly selected households in Canada will receive the 36-page long-form questionnaire known as the National Household Survey, while the remainder of Canadians will receive the 10-question short version. Both are mandatory.
Under Section 31 of the Statistics Act, the consequence for failing to provide information to a mandatory census or falsely answering is liable to a summary conviction carrying a fine of up to $500, imprisonment of up to three months, or both.