Canadian Car Seat & Booster Seat Legislation (by Province/Territory)

from Safekids Canada:

British Columbia
Effective July 1, 2008
Children must ride in a rear facing car seat until they are a minimum of 20 pounds (9 kg) and at least 1 year of age. Children who are at least 1 year of age, at least 20 pounds (9 kg) but less than 40 pounds (18 kg) must ride in an appropriate car seat.
(NEW) Effective July 1, 2008
Children must ride in a booster seat until they are a minimum of 4 feet, 9 inches (145 cm) tall, or a minimum of 9 years old.

Alberta
Children must ride in a car seat until they are a minimum of 6 years old or over 40 pounds (18 kg).
NO PROVINCIAL BOOSTER LAW

Saskatchewan
Children must ride in a car seat that is appropriate for their size until they are a minimum of 40 pounds (18 kg).
NO PROVINCIAL BOOSTER LAW

Manitoba
Children must ride in a car seat until they are a minimum of 5 years old and a minimum of 50 pounds (23 kg).
NO PROVINCIAL BOOSTER LAW

Ontario
Children must ride in a rear facing car seat until they are a minimum of 20 pounds (9 kg). Children who are at least 20 pounds (9 kg) but less than 40 pounds (18 kg) must ride in an appropriate car seat.
Children must ride in a booster seat until they are a minimum of 4 feet, 9 inches (145 cm) tall, or a minimum of 80 pounds (36 kg), or a minimum of 8 years old.

Quebec
Children must ride in a car seat or booster seat until they have a minimum seated height (measured from the seat to the top of the head) of 25 inches (63 cm). The car seat or booster seat must fit the child’s height and weight.

New Brunswick
Children must ride in a car seat until they are a minimum of 5 years old or more than 40 pounds (18 kg).
Children must ride in a booster seat until they are a minimum of 4 feet, 9 inches (145 cm) tall, or a minimum of 36 kg (79 pounds), or a minimum of 9 years old.

Nova Scotia
Children must ride in a rear facing car seat until they are a minimum of 22 pounds (10 kg) and at least 1 year of age. Children who are at least 1 year of age, at least 22 pounds (10 kg) but less than 40 pounds (18 kg) must ride in an appropriate car seat.
Children must ride in a booster seat until they are a minimum of 4 feet, 9 inches (145 cm) tall, or a minimum of 9 years old.