This is not true. The town of Radisson was built in the 70s during work on the James Bay Project and is still mainly francophone. It's about 2° north of Dunkirk.
It is predominantly French speaking, is 1° further north than Dunkirk, is incorporated as Ville de Fermont, has a population of about 2400.
It also has a Wikipedia page that claims "Fermont is arguably the world's northernmost Francophone settlement of any considerable size": https://en.wikipedia.org/wiki/Fermont.