Public Health Agency of Canada spokeswoman Jirina Vlk says seven people were ill Tuesday on a flight that landed in Ottawa.
The sick passengers had vomiting, diarrhea, nausea and fever.
On Thursday, 20 passengers on a flight from Cuba to Toronto's Pearson International Airport had the same symptoms.
On Friday, there were 12 ill passengers who landed in Ottawa and two of them were sent to hospital.
Another plane landed Friday in Toronto with 14 sick passengers.
Vlk says there's no immediate word on what caused the illness.
Three of the flights were operated by Air Transat and one was Sunwing.
Note to readers: This is a corrected story. An earlier version said the agency called in was Health Canada and only referred to three flights.