It's also a very important question. Anyone who interacts with the RCMP or the CBSA, regardless of whether they are in detention, is able to file a complaint, so in the hypothetical that you have posed, yes, a detainee could make a complaint if they believe they were mistreated by a member of the CBSA. That, too, will allow for a fact-finding process, if that is what the commission chooses to embark on, and then the making of recommendations.
On May 30th, 2023. See this statement in context.