In Canada, is a welding engineer certified by the Canadian Welding Bureau required to inspect every weld job? Does a building need to be bigger than a certain size before you have to hire a welding engineer to perform an inspection of the field welds? Can a structural engineer perform these inspections in lieu of a CWB certified welding engineer? When are we mandated to have a CWB certified welding engineer perform these inspections? Is all welding required to be performed by a CWB certified welder? Do all fabrication shops require to be CWB certified? Thank you.

In Europe, this is covered by the EN 1090 code.
Depending on several factors (type of steel, stainless, alu, ... - thickness of the plates - fatigue loading or not - type of building (private, public, ...) - consequence cless (could someone die if the weld failed)
you have to follow welding coordination (IWS, IWT or IWE) as specified by the code.

You will probably have an equivalent code, someone will surely know which one...

In Canada you should first start with CSA S16 for structural steel. S16 then refers you to CSA W47.1 & CSA W59-03. W59 then sets out CSA W178.1 (Inspection Companies) and CSA W178.2 (Visual Inspectors). The CWB Group are the ones that facilitate certification of Inspection companies and Inspectors.

I think you mean to say CWB Welding Inspector NOT CWB Welding Engineer.

Yes, all welding needs to be performed by a CWB Certfied Welding Company, using CWB Certified Welders using CWB stamped Weld procedures and finally a CWB Inspector (CSA W178.2) preferrably working for a CWB Inspection company.

If you need some help, I can contact you off-line regarding inspection companies available for your needs.