The short answer is, in BC the customer decides which of the vehicles’ drivers is primary.
Take for an example, a vehicle driven by both husband and wife. The wife drives the vehicle 5 days/week and the husband only uses it on the weekends. The husband drives many more kms than the wife does. Is the wife primary driver because she drives the vehicle more based on time, or is the husband the primary driver because he drives more kms? Insurance brokers are advised by ICBC to have the client make this decision on their own, brokers cannot tell the client who to choose as primary driver.