I mean, Scott Bowman is the "winningest" coach in NHL history, right?
Let's see, he coached a new expansion team (St.Louis) to the top of the expansion clubs (when 50% of the NHL was expansion teams) and therefore into the Finals in each of its first three seasons.
He then coached Montreal for eight years, going .744, and winning five Stanley Cups.
He then coached/managed Buffalo for seven years, with the team going .594.
He then coached Pittsburgh to its second Stanley Cup, followed by its greatest-ever regular season, going .628 in two years.
He then coached Detroit for nine years, going .655, winning three Stanley Cups and four Conference championships.
So: Nine Stanley Cups with three franchises in the post-expansion era, and a career record of (pre-Bettman inflated) .657 in thirty years behind the bench (That would be around .710 today for thirty years' total).
I'd say that's your hands-down winner, although cases can be made for Toe Blake, Al Arbour, and a couple of others. Bowman's only minor disappointment is the final game of the '81 Canada Cup, and the relative good-but-not-greatness of the Sabres after the early-80s.
But when you're the best coach in 1968 and still the best coach in 2002, you win hockey.