Unlike almost every other country, and something we learned from the Swiss, almost all of our laws / regulations / licenses are determined by governmental bodies other than the US Government.
For electrical work, the matter is decided by each State .... and, in many cases, the States pass the responsibility down to the town or county. There are even places where not even as electrical contractor is required to have any license at all!
Canada is extremely similar to the USA, at least in terms of the hardware used. There are many differences in the specific codes- but nothing like the differences between Canada and the rest of the world.
If you belong to a trade organization or Union, it is very possible that they have some sort of arrangement with a similar group here.
Otherwise, when it comes to 'work' visas, the USA tends to vary it's rules to match where you are from. In your case, that means getting hired before you come here to work, getting the work visa while outside the USA, etc. The prospective employer will be expected to fill out mountains of paperwork on your behalf.
Most places will not let you take the local license exam absent work experience that they can verify, completion of an apprenticeship they recognize, etc.
"Instrument Fitter" sounds like something done by the members of the ISA - the Instrumentation Society of America. I suggest you look to them as a source of certification, etc.
If you can qualify for their certifications, it is very possible that willing employers can be found, and you will be able to take advantage of special visa rules, intended for bringing "Professionals" here on a temporary basis.