I don't think it will be required at landing time. Once you get to Canada and get your health care in place, you look for a family doctor or if you can't find one, go to a walk-in clinic. The doctor will look at what vaccinations your children have had and what they need and get them up to speed.
You can see at
http://www.caringforkids.cps.ca/immunization/VaccinationChild.htm#table1 what kids in Canada usually have for vaccinations.