It's just a fact I've heard a few times but more Canadians shoot left handed then right handed, while more Americans shoot right handed than left handed. And it does make sense too if you look at the roster for the 2010 Olympics.
http://www.nytimes.com/2010/02/16/sports/olympics/16lefty.html
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“The top hand on a hockey stick has to be able to handle the torques of a stick while the bottom hand just has to handle the weight with no torques,” he wrote. He theorized that American children, who tend to take up hockey when they are older and bigger, can afford to put the stronger hand, generally the right, on the lower part of the shaft for more precision.
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i agree with this. growing up, i played street hockey with about 15 immigrant kids, all of who have picked up the game at an older age, let's say over 12
everyone shot right except two naturally left handed guys and one kid's younger brother
so i do think if you begin playing hockey at a younger age, you're more likely to shoot left (or right if you're naturally left handed), because the stick is easier to control if your dominant hand is on top.
if you're older and able to control the stick with the left hand, you'd tend to focus more on trying to obtain more power from your lower hand, thus you'd shoot right.