The league could have been 200% Canadian back in the Original Six days and it'd still be way easier for a Canadian hockey player to crack the NHL today vs 60's.
Say you're the 100th best Canadian hockey player today vs O6 days. Nowadays you're a star. Third or maybe fourth best Canadian on your team. Back then you'd likely not crack an NHL team roster. Okay you might get in, as a fill-in, or a fringe player.
200th best? Nowadays you are still a millionaire and you have a steady job in the top league in the world, likely a long career, average Canadian NHLer (2ooth out of 300). Middle six, or middle pair, probably. Back in the day? You'd not even be a very good minor leaguer. Ride the bus and hardly make a living wage. Expansion to 12 teams suddenly gave you a (long) shot at making the NHL. But the competition would be insane, even then.