I used to work for StatsCan about 20 years ago. This was before the Harper reign of terror, so I'm not sure if anything's changed, but with that caveat -
Stats Can has to create its own list of households to mail the census to. They are very concerned with even the appearance of sharing personal data* between government agencies, as that could result in people providing false data to maintain anonymity.
They don't get their data from Revenue Canada, or anywhere else, even though it would make their life incredibly easier, and cost less. Privacy and quality of data are things they take extremely seriously.
*NOTE: Obviously StatsCan releases its data in reports. But, once census data is combined, it gets reviewed before publication to ensure that it isn't possible to statistically reverse-engineer the data and identify anything personal about that area. For example, if there is one person of a particular religion in a neighbourhood, that particular type of data would get rolled up and combined with other neighborhoods so that one person isn't identifiable from the census data.