.. or what Service Canada can legally expect to have answered.

I have worked overseas for decades and coming back to Cda find that it is a bit of a hassle to update my 'dormant' SIN. I don't mind proving my identity with my birth cert, passport and driver's license - but I find requests beyond that to be intrusive. I wonder if they are even illegal (to be asked I mean). For example, as long as I can prove my identity with basic ID, why is it any of their business where I was or what I was doing for so long? Specifically, I find requests for all my employers and residential addresses for the past 5 years to be a violation of my privacy.

What, if any, are the limitations that privacy law permit when it comes to dealing with the Federal gov't?

   

There are none. The government is the only one to whom you should give your SIN. The government is under some new and very strict privacy laws.

http://www.privcom.gc.ca/legislation/02_06_01_e.asp

Every other entity that asks for it should be denied.