It's a deal.
This issue is often raised in connection with tribunals. There's no guarantee that any selection process will be perfect. But in my experience with federal tribunals, political interference is a non-starter. Certainly, that was the case in my own tribunal when I was at the CITT, and I think it's more common than that. It's simply understood that this element of independence must be guaranteed.
The selection of individuals is still a process that goes through cabinet, I understand. Names may be brought forward. Selection processes differ from tribunal to tribunal. I can't speak to that question with any expertise. Really, my knowledge of this is anecdotal, rather than general.