Clearing custom at PEK should not be very time consuming,unless your flight is too late so that you may miss your 3 hour layover time window.
However, if you miss the connection on you separately purchased ticket,you might end up losing your ticket value or at least paying much more on your PEK->CAN portion.
However, if you miss the connection on you separately purchased ticket,you might end up losing your ticket value or at least paying much more on your PEK->CAN portion.