It’s not a grey/gray area. That type of evidence is hearsay.
Under the principled approach, internet postings are not always excluded as evidence if it’s deemed as reliable and necessary. But generally there must be a lot of other evidence lawfully collected by the police using police powers. This particular evidence alone as described by CBC wouldn’t likely be sufficient to obtain a conviction especially since it was obtained by illegal means already contrary to the criminal code. (Unauthorized access to data). Further, if CBC accessed private communications as seems to be the case here there’s a good civil tort waiting for them.
In point of fact, actual admissions of guilt to indictable offences - made online - have been excluded as evidence just as often as such evidence is admitted. For example, in one case in Ontario the kidnap and murder if a young girl the BBM messages (and images) between accused admitting their involvement were captured and stored by an internet provider, and then produced to police under a search warrant, and then subsequently excluded by the trial court. Conviction was obtained using other evidence. It was found the provider had no lawful authority to collect and store the content of messages.