It may have been years ago that CAIL sold one or two to WS [and likely through a third party]. But for that last few years WestJet has only been in the market to buy brand spanking new -700s.

If WS has some of the old CAIL equipment then they will be called:
737-275 if they were ex PWA
737-217 if they were ex CP-Air
737-296 if they were ex EPA
737-2L9 or 2T5 or 2T7 or ....
there comes the headache again.