Upvote:4
Your husband's relative is also your relative. Unless they explicitly ask for proof of the relationship, you don't need to provide it.
Also, a "sponsor" is not mandatory, nor is one even helpful in cases such as yours where you can afford to travel to Canada on your own. Your visa application would be just as strong if you were visiting a friend who was no relation at all, or indeed if you were just traveling to Canada for some sightseeing on your own. In fact, it might even be stronger without a relative in Canada, because the officer would be less likely to suspect that you would want to stay in Canada.