The route was IdleWild (renamed JFK in 1963) or LaGuardia -> Gander, Canada -> Shannon, Ireland -> Paris. The trip took a total of about 18 hours going eastbound with tailwinds, and 24 hours going westbound with headwinds.
Gander was opened in 1938 and still is the preferred refuelling stop for aircraft that can't make the hop across the Atlantic in one go, simply because it is the easternmost point on the North American continent where such a facility could be built. For a while it was the largest airport in the world, and was used extensively by the military during WW2 as a stopover point for aircraft being ferried to Europe.
Air France used the route from the beginning of their transatlantic service in 1946 until the late 1950's, when the jet age made it possible to fly the route non-stop.