The greatest number of complaints does not necessarily mean the biggest offenders, but right now we know that the organizations with the greatest number of complaints are the RCMP, the CRA, and I believe the next one is Canada Border Services Agency. The reason is simply that these organizations have the greatest amount of personal information, so it is normal that we'd have the largest number of people asking for their personal information from these organizations.
On November 8th, 2006. See this statement in context.