On 1 June 2013, the 1921 Census will be transferred to Library and Archives Canada and will be made public shortly after that date. Estimated availability dates haven't been published yet. I wouldn't expect the Canadian 1921 census to be available on the morning of June 2, but it should appear on the Web within a few months after that date.
You can learn more in a new Wikipedia page started by Helen Riding at http://en.wikipedia.org/wiki/Canada_1921_Census. That page also contains links to several other web sites. Of course, as with everything on Wikipedia, if you have more details than what is already posted there, you are invited to add your information.