Free overnights transiting Canada

The London, Ont Flying J just off the 401 at exit 189 has a designated RV parking area where folks overnight.

The Walmarts in Ontario are virtually the same as in the U.S. Most allow overnight parking (depending on local regulations).
Any of the rest areas, service centres, will have overnight parking available, some even have designated RV sections. They are different than the one in U.S. because they are a commercial stop. Onroute Ontario.
There are also various truck stops at the interchanges along the way.

Hint, don't plan on getting of the highway in the Greater Toronto area (Milton to east of Oshawa) Just TOO busy and probably not easy to get back on the highway. Also avoid rush hours 6:00 - 9 am and 2:30 til 7pm. The rest of the times, it will just be very busy.

Ken

Plenty of rest area's along the 401 after you get off the 402 at London but they are truck stop's and will be noisy. Just my thought's.

You do realize you will be traveling down the busiest freeway in N. America in the most populated area of Canada.
Saying that in case you thought you were passing through the boonies.

Ask, especially at Wally World's in Canada. Granted Canadians will shop at Canadian Tire stores before they go to the USA chain.

:p