Actually, I think I got the 20,000 to 200,000 figures from one of the reports done by CIC several years ago, so I'm not sure how accurate they are. I guess they looked at the number of removal orders being issued, and tried to calculate how many of those were actually executed. I've heard numbers as high as a million, so I'm not quite sure, although 200,000 sounds reasonable and realistic to me.
Certainly in cities like Toronto and Vancouver, almost every single person I know is aware of at least one person who is undocumented--and I don't think they're all the same person.