I'll answer your second question first. If Canada were to sanction an actor without the support of either the United States or the European Union, the effect would be pretty negligible. Obviously, that person would presumably still be able to do business in most of the major financial centres of the world. It wouldn't necessarily alter their behaviour all that much.
In terms of sanctioning individuals within authoritarian countries, you're correct that most of the targeted countries where sanctions have been imposed have been authoritarian or totalitarian. You're also correct to infer that most of these targeted individuals presumably have the support of the state. Indeed, that's usually the idea of it. The idea behind a lot of these sanctions is that in some cases you're trying to prevent corrupt or criminal liability, but in other cases, what you're trying to do is, in fact, pressure the very people who presumably have influence over an authoritarian government, which is sometimes a relatively murky question, as opposed to presumably a more open democracy.
That said, I should also point out that one of the drawbacks, even in the cases of these kinds of targeted sanctions over the last few decades, is that there is significant evidence that when they are imposed against an authoritarian state, one of the responses of the authoritarian state is to repress even further, which is to say that usually the authoritarian state becomes even more authoritarian in nature in response to any sort of external acts of economic coercion. That doesn't necessarily mean that, alas, you could eventually potentially hope for regime change, or once the sanctions end, that could ease up, but that is without question an important negative externality to consider.