Likely the NHL still wins. The Habs like any other original 6 back then have the advantage of knowing each other well and not needing to work on their chemistry because they already have it, look at the New Year's Eve classic between Montreal and the Red Army in 1975. You've still got a league however that has Hull, Mikita, Howe, Mahovlich, etc.
It is worth noting, that back in the day the Cup winners played the All-stars and this was the first year it was moved to the middle of the season. So the game was played in January. The Habs won that game, but it can also be noted that the Leafs the following year played the NHL All-stars and won too and they were a different team in 1968 than in 1967.
But in a 7 game series I think you lean on the team that has the depth and that would be the All-Stars. The 1966 Habs were far from their most dominant and in reality were down 2-0 to Detroit before winning the last 4 games and needing a really controversial overtime goal by Henri Richard to win the Cup, or at least prevent a Game 7.