Not a clue about Norway. Somebody expressed an interest in Ireland.
The UK probably Ireland and it will vary with other EU countries.
You can’t use a Canadian or probably an American certificate. You will require a national flag state certificate.
Not a big problem, you have to apply for a certificate of equivalence.
Most of your US or Canadian certificate requirements will be accepted. Provided it is an STCW certificate and course.
Eg For Canadians a unrestricted WKM, Will get an equivalence for UK Class 4.
The restricted or near coastal WKM as far as I know will not get certificate equivalence.
There is a UK class 5 which is home trade and restricted tonnage.
You also have to prove proficiency in English. Should be a problem.
Higher level certificate may require an exam on Business and Law. Regulations being different.
Obviously you will also have to qualify for residency or work permits.
I know quite a few Canadians who have done this to accrue sea time. Which is hard to obtain in Canada.
I believe It is similar for the engine room. Unrestricted Engineer Officer of the Watch or 4th Class. Engineer and above.
Before all this Brexit stupidity if you had a British or EU parent or even Grandparent you could get a passport band work in any EU country.
What effect Brexit had. who knows.
If you have an Irish connection the EU is still all possible.
I don’t think Norway is part of the EU but it does have some kind of deals with EU.