Saskatchewan is the only province that recognizes the internationally recognized National Board registration system as an acceptable alternative to CRNs, although an additional Saskatchewan filing fee also has to be paid per vessel. [Update: Saskatchewan now only accepts National Board as an alternative for registration on used vessels]. Vessels that are CRN registered can also be National Board Registered if desired. If a vessel is built outside of Canada for Canadian use, it must be both CRN registered and National Board registered.

From B51-14 page 20 4.10.1.2:

Manufacturers in countries other than Canada that manufacture and export boilers and pressure vessels to Canada shall ensure that all boilers and pressure vessels are stamped with the appropriate ASME Code product certification mark and registered with the National Board.

Key Point: Fabricators outside of Canada must also register with National Board.

Updated Nov 2015, for Ontario:per Ontario’s Code Adoption Document (BPV-13-01, 1.20): Registration with the National Board of Boiler and Pressure Vessel is not required (applies to Ontario only).

Those who take a historical interest in rules and regulations would find strong correlation between Canada’s current system and the American system before the development of the National Board registration system in 1919-1921. History of National Board