As long as the police don’t detain, arrest or charge the person, they do not have to caution the person. (And there is such a thing as investigative detention – stop and frisk – that usually does not require that a caution be given.)
Once they have detained (other than stop and frisk), arrested or charged the person, then they must caution the person, but provided the person is given reasonable opportunity to seek counsel, the police can continue on with thier interrogation without the person’s lawyer being there. (Note to all you yanks, this is a Canadian rule. YMMV.)
Thus you get mooks incriminating themselves and then getting arrested (no requirement to caution), and you get arrested mooks being cautioned and then incriminating themselves while the interrogation continues without their lawyer being present.
Another interesting issue is what to if the mook says something self-incriminating while being arrested (usually the mook is SOL when that happens – the police don’t have to put the arrest on hold to caution the person).
Assume you don’t have the little girl under lime in your basement:
Would I really be a suspect simply because I asserted my right under the 4th Amendment? (Yes I know the OP is in Canada but I’m in the US). Oh pleeeeeeese Phoenix PD. Pleeeeease harrass and maybe arrest me simply because I didn’t let you into the house without a warrant. I will retire off of the money I will win from you in the lawsuit.
Unless I’m convicted for murder because I pled the 5th.
The point is not that they will not inform you of your rights if you are arrested. It is that if they are wandering around your home looking for clues in a case that you are not part of, they can find something that can lead them into suspecting you of another crime. They have no reason to tell you of your rights if you are not yet under suspicion. So while they are there ,they can say you said something that to you was harmless. You have no gain by dealing with cops if you do not have to. You have possible harm.