A. Ontario Building Code Sentence 7.6.2.2. (1) requires: "Every potable water system that supplies a fixture or tank that is not subject to pressures above atmospheric SHALL be protected against back siphonage by a backflow preventer."
Ontario Building Code Sentence7.6.2.3.(1) requires: "...where a backflow preventer is required by this subsection, the backflow preventer SHALL be selected, installed and tested in conformance with CSA B64.10, "Selection and Installation of Backflow Preventers".
The CSA B64.10 classifies Trap Seal Primers as "Severe Hazards". The CSA B64.10 tells us that the ONLY suitable means of backflow protection for this degree of hazard is an RP backflow preventer, Pressure Vacuum Breaker or an Air Gap.