This is sort of misleading.
First off its the king of canada, which technically is a separate position that just happens to be held by the same person (personal union), with same succession rules, and also a treaty where everyond is supposed to agree before changing succession rules.
More importantly it is a constitutional monarchy. The crown can't just do what it pleases but is bound by the constitution.
A big part of that is the king must listen to the advice of the prime minister/the privy council, and that the prime minister must have the confidence of the legeslative branch.
In practise the king lacks pretty much all power. There are a couple edge cases (fire the governor general maybe) and still a lot of soft power, but he is essentially a distant figurehead.