The answer is known- exposure to genetically modified organisms (GMO) and chemicals tossed into food, upon arrival in Canada. Allergies take several years to develop.
Check the statistics from 20 or 30 years ago, there were much fewer allergies than there are now - food allergies were limited to crustaceans, strawberries and pollen.
Allergy to peanuts was almost non-existent and then suddenly exploded. About the time of mass arrival of GMO food.