It's not "their playground". Besides the fact that the South China Sea is a crucial international trade route (and thus shouldn't "belong" to anyone), it is also bordered by many nations other than China, like Vietnam, Taiwan and the Philippines. And these nations are very bothered by the way China is using its size to bully them out of their own coastline. That is why Canada is there, to prevent China from dominating the smaller states. Obviously NATO has more than one goal in the region, but they are not uninvited guests and, in a world as globalized as ours, the South China Sea might as well be Canada's playground.
Yeah I saw that and it immediately discredited the rest of the article. You can't cry about US imperialism while handwaving Russian imperialism.