I fly Air China from Harbin to Beijing Capital Airport. Then fly Air Canada PEK to Toronto.

Hi. It is a domestic to international transfer both in T3 at PEK. You don't need to collect the luggage at PEK. Hereunder is the correct procedures:
Flight Arrival & Transfer Procedures - Inspection & Quarantine - Exit and Entry Frontier Inspection - Security Check - Customs inspection - Waiting & Boarding