For those doing this: here's how to correctly follow the advice, and not do pointless, idiotic, extra steps. Go to the IRCC webpages and check, using the 'get my application package' part here:
https://ircc.canada.ca/english/information/applications/spouse.asp
Select what type of application package (eg sponsor spouse and dependent children), then countries that are applicable (where the spouse and/or children live and for countries issuing the documents of importance (they are listed eg birth certificates, passports, etc).
As an example of a country that does require specific notarial or other steps, Colombia, here's the text (on document procedures):
Colombia
- Copies of all needed civil documents must be notarized by the notary’s office (“notaría”) where the documents were registered.
For countries that do not have specific additional document instructions, it will be something like this: eg "France – Instruction(s) for documents - There are currently no special instructions for documents for this country."
Note, in SOME cases the IRCC instructions may specify something (as in Colombia above) that is difficult to do from abroad, and there may be some alternative - like getting docs authenticated at the country's Embassy, or via some other mechanism (possibly apostilles under Hague Convention). IRCC does not always have perfect up to date information. Up to the applicant to look into it (and deal with it if not accepted by IRCC).
But they do NOT require steps like authentication if they don't ask for them.