Yes according to this
http://www.dgip.gov.pk/files/immigration.aspx, Pakistani government recognizes the Pakistani-Canadian dual citizenship.
Consequently yes the procedure is to show the Pakistani passport to onboard the first flight and with Pakistani customs. Then on the return flight show the Canadian passport to onboard and with Canadian customs. You also need to choose a passport for the plane reservation and here you may choose any.
In case the other country didn't recognize dual-citizenship then that would be more tricky, if not illegal.
Edit: On the link above it also states "Any citizen of Pakistan residing outside Pakistan, who is not a minor and is also a citizen or national of another country or has been given by the competent authority of another country any valid document assuring him/her citizenship or nationality of that other country, shall make a declaration of renunciation of citizenship on form “X” in triplicate to the Directorate General Immigration & Passports Islamabad through Pakistan Mission abroad."
So I'm not completely sure that Pakistan actually recognize dual citizenship, you may need to check that.