I just checked the application guide as well,it doe not say the Police Certificate have to be an original copy. But as you have said here, he/she needs to check the country specific requirements, to check and see if for that specific country, they require an original copy for any specific document. You are correct to say that won’t require original copies unless they deemed necessary, and it is specified usually.
I don't know what IRCC will do with this, and yes, generally, they specify if they need an original.
BUT: I do not understand why anyone would submit a photocopy of the police certificate (and employment letter for that matter).
These are NOT documents that anyone has or obtains for any other purpose than for applying to IRCC. There's no value to keeping them until later. This is NOT like marriage or birth certificates where one has good reason to retain the 'original' or is likely to have any use for afterwards (if you want, keep a photocopy or scan for yourself).
Also keep in mind: the only people likely to tamper with or fake a PCC are precisely those who have a criminal record. So ... you might logically expect that they would prefer an original.
So for both of these: follow the instructions. But for both I'd also say - submit the original, you applied for and got it specifically for applying to IRCC and it will have zero or little value in any other context.
*Two small points: sometimes when IRCC asks for an original eg of a divorce decree or marriage certificate (for certain countries) the meaning of "original" includes a duplicate
issued from or by the civil registry (or equivalent). Usually that means on special paper.
For police certificates, these are increasingly done online in lots of countries and eg you may get an electronic version where IRCC specifies 'original'. There's nothing to be done in such cases except print and send, with an explanation if you feel necessary. IRCC will accept if that's how it's done. Sometimes it takes a while for IRCC to catch up to developments in all countries. But: it would still be a bad idea to send a photocopy of that printed electronic version rather than the original print - no sense confusing them.