バスと一緒で、乗客として乗る場合は大丈夫です。
http://www.mto.gov.on.ca/english/faq/safety.shtml#SEAT4
Are any drivers/vehicles exempt from the child safety seat requirements?
Yes. The following are exempt:
The driver of a taxicab, bus or public vehicle, while transporting a passenger for hire.
Taxi drivers are exempt from the child car and booster seat requirements when transporting a passenger for hire.