Is there an online source for Canadian Instrument Approach Procedures?
Not officially, no. The official approaches are available in a PDF format to download for 20 CAD for each volume.

However, FltPlan.com claims to provide free, up-to-date charts:


  In cooperation with Nav Canada, FltPlan.com is pleased to announce
  free Canadian Approach Plates, also know as CAP (Canada Air Pilot).
  These online charts include all instrument approaches, airport
  diagrams, SIDs, STARs, and special use approach plates for Canadian
  Airports. They work similarly to the already available U.S. approach
  plates.
  
  CAP is an extension of FltPlan.com's continuously expanding coverage
  of Canada, Mexico, Latin America and the Caribbean. In May of this
  year, we expanded our coverage to include the filing of IFR
  intra-Canada flight plans. The availability of free, online Canadian
  Approach Plates brings a new level of safety and convenience for
  pilots in the planning stages of their trip.


Though I have not seen anything from Nav Canada stating that this is "in cooperation with Nav Canada", they do seem to be an authorised distributor of paper charts.

Note FltPlan.com warns that these charts shall not be printed as a replacement for "proper" paper charts -- I am not sure whether these are deemed to be official or not, but it is rather unlikely.