Per the Hockey Canada Rule Book

A game is considered tied if, at the end of the three regulation periods, both teams have scored an equal number of goals.
Overtime periods will always be sudden-victory, meaning that the game will end as soon as a goal is scored.
Members and leagues may make their own rules regarding overtime for games under their jurisdiction.

6.17 (a) If the game is tied, the following will occur:
          i. If the Official feels it is necessary, they may order the ice to be resurfaced at the end of the three regulation periods.
          ii. The puck will be faced-off at centre ice and the play will continue with a 10-minute sudden-victory overtime period;
          iii. If the score is still tied after the 10-minute sudden-victory overtime period, the teams would take the normal between period break and return to play a 20-minute sudden-victory               period. Note 1: The teams will only switch ends if the ice is resurfaced.