This shouldn't be a problem. I presume you are scheduled on CA 998 YVR-PEK connecting to CA959 PEK-BKK. At YVR check-in, you should be able to get boarding passes for both flights and have your bags checked all the way through to BKK.

For this sort of transfer, Customs will be irrelevant for you. Immigration will not be done at the regular desks but at a special "international transit" desk which you should easily spot. You'll show passport and onward boarding pass then be directed to security screen then back airside. That's pretty much it. For an on-time arrival, you should be able to complete all this, include the necessary walking, in 30-40 minutes. Do try to get a seat reasonably forward in the cabin on the TPAC flight so you can deplane and get to the immigration area fairly quickly.

Plan B in case of trouble: If for any reason you are really late in (such as late departure from YVR), putting your BKK connection out of reach, then immediately go to the transfer desk at PEK, just before Immigration area, and see if they can reissue boarding pass for the later PEK-BKK flight CA 979. If they can't do it there, they'll likely tell you to go to Departures on the nonsecure side to Air China for them to reissue you on next flight. In this case, you need to look for the TWOV (Transit Without Visa) Immigration queue which will get you stamped out to go landside. No visa needed for this sort of thing.