Personally, I vote the UN or some other equivalent international body. On the one hand, I understand that Canada's actions can affect other countries, and certainly mankind reserves the right to to defend it fellowmen living within our borders if those persons are being persecuted, or if Canada itself is hurting people beyond our borders.
However, I also believe in order in all things. It's not up to any one country to be judge and jury against Canada and take the law into its own hands, as that would be plain imperialism. However, the international community, through appropriate international bodies such as the UN, would certainly be allowed to criticize Canada, place sanctions against Canada, or even attack and invade and occupy it if it was a decision made by the world in defense of the wellbeing of the world and not just one country's or a group of countries' 'national interests'.
And of course, since I don't believe in double standards, I believe the same ought to apply across the board, and we ought to treat other countries the same we we would want to be treated by them.