Thank you for the question. That's in fact exactly at the heart of the experiment that the United States conducted. We get a given percentage of response—in their case, in the low nineties—from a mandatory census.
What percentage would we get in response to what's called the “American community survey” if it were on a voluntary basis but we explained the purposes and strongly encouraged people to respond?
The answer is that without arduous follow-up the percentage point difference is about 30%. So if you're assuming that the only difference is whether it's mandatory or not, the answer is about 30% of Canadians.
I think, in part, it's not that 30% of Canadians are dragged kicking and screaming, but rather, part of its being a mandatory census tells those respondents that your country really cares and this is very important to do. So I think some proportion of that 30% reflects their response to the government saying this is important, it matters, and you must fill it out.