The "safest" way is to book two separate nested itineraries. Assuming you're a Singaporean citizen, you'd book the following (e.g, and replace with relevant nationality Malaysian, Indonesian etc.):

Vancouver - Hong Kong - Vancouver (depart Jun 21, return Aug 15)
Hong Kong - Singapore - Hong Kong (depart Jun 22, return Aug 15)

On the outbound, this would turn into YVR-HKG-SIN: YVR-HKG with your CA passport, and HKG-SIN with your SG passport. Hong Kong doesn't require a visa for either citizenships. On both sides, it looks like you're just going to/from HK for a long stay (depending on where you're resident) and there's no need to display both passports on either ticket. Hong Kong doesn't stamp passports either, so it makes it a little easier to explain the lack of stamps. Of course, you'll need something else for any further questions.