http://www.worldjunior2014.com/en/information/tournament-format/
I believe this is the format. Essentially it would come down to plus minus in the games between those three teams. If teams are tied in plus minus, it comes down to total goals scored in games between those teams.
USA finished its games against Sweden and Canada +1 with 4 goals.
Essentially, Canada needs to beat Sweden by 3 to win the group. Canada beating Sweden by 1 would see USA win the group, Sweden finish second and Canada third. Canada beating Sweden by 2 would see USA finish first, Canada second and Sweden third. Obviously if Sweden wins they are first since there is no tie.