The problem with defensemen is skating. Too few have speed, great balance on their skates, and ability to handle the puck. The result is being forced to back in and concede the zone to the oncoming attack instead of blunting the attack at the blue line, inability to take possession of the puck because of lack of speed, and the inability to safely clear the puck out of the zone and/or launch an attack up ice because of the inability to handle the puck.
Throughout the WHC (not just against Canada) we saw opposing teams continuously cycle the puck in the defensive zone, blasting away shot after shot on goal. Eventually, they start going in! Smaller ice doesn't fix the problem - IMO it makes it worse, because it diminishes the need for speed and quickness, and relieves them of responsibility for clearing the zone under control.