I can't speak with absolute authority, but I know that our screening officers, under the Quarantine Act, can refer someone to a quarantine officer under PHAC. The individuals must wait until they've been dealt with by that quarantine officer, and only at that time can they depart the CBSA hall. I would have to come back in order to be authoritative on your question.
Evidence of meeting #2 for Health in the 43rd Parliament, 1st Session. (The original version is on Parliament’s site, as are the minutes.) The winning word was china.
A video is available from Parliament.