Not all 26 letters of the alphabet appear on BC license plates. The exceptions go all the way back to 1970, when BC switched from issuing sequential plate numbers to an alphanumeric system.
I would have guessed that I and O would need to be excluded , but I did not expect that they'd have to exclude more letters due to the manufacturing process! I assume they chose to exclude Q since it also kind of looks like zero and U to minimize the number of unusable plate numbers containing rude words, but it looks like Y and Z missed out just because they're at the end of the alphabet.
BC has issued several different plate series since the '70s — BCPl8s has the details if you're interested — and the manufacturing process has presumably changed since then, but I believe the letters have remained the same: to this day, I have still never seen an I, O, Q, U, Y, or Z on a passenger car. 
British Columbia Passenger License Plates 1970 - 1978. BCPl8s. Christopher Garrish (2014). ↩︎
There's a relevant xkcd. ↩︎
Keep an eye out for other types of vehicles, though. Motorcycle plates starting with U, Y, and Z were issued in 2012–14, 2017–18, and 2019–20 respectively, and the letters can also be spotted on plates assigned to commercial trucks. ↩︎