Cyufjy

I recently renewed my passport. I also have an expired passport which has my Canada visa (visitor's) valid for another three years. I have already used my Canadian visa which is multiple entry. I am planning to visit Canada this summer.

Since my valid Canadian visa is in my old/expired passport, do I need to renew/transfer my Canada visa or can I simply travel with valid visa in old passport?

Do I need to renew/transfer my canada visa or can I simply travel with
valid visa on old passport?

You don't need to transfer your valid Canadian visa on your fresh passport. You can simply attach your old passport with your new one and can travel to Canada. Answer is from official Immigration And Citizenship EN4 Port Of Entry Examinations:

13.18 Valid visas in expired passports

Visa officers will not put a visa in an expired document and will not
issue a visa for a period surpassing the expiry date of the passport
or travel document. Occasionally, documents containing valid visas are
cancelled or replaced. If a valid visa inside an expired document is
presented at the POE along with a valid passport or travel document,
the visa is considered valid.

Therefore you will be fine and can simply travel to Canada with valid Canadian visa on old passport along with a valid new passport.

Yes, I have already faced the same issue 2 years ago. I emailed and called personally Canadian High commission in Manila and they replied with the same answer. I can also confirmed that my last two visits, I never faced any issues with neither airlines nor with Canadian Immigration.

If you have a valid Canadian visa that was placed inside of a previously valid passport or other travel document that has since expired, and you also have a new/renewed passport or travel document from the same country with the same identification number (e.g., the same passport ID number), you can usually present the expired travel document containing the valid Canadian visa, together with the new/renewed travel document lacking a Canadian visa, at the Port of Entry in Canada. You may, however, want to confirm this with Canadian immigration officials or an authorized Canadian visa expert to be on the safe side.