What's wrong with that? You aren't entitled to freedom of expression on any particular platform run by a private entity. Freedom of expression only applies to the government.
Sure, it doesn't violate the constitution but it still is a serious issue.
I can just hear it now... what's the big deal the Canada Post is under no obligation to do business with you.
No. For a place of discourse to become major requires a large amount of people to be actively involved. I can't just "form my own" because for it to be major other people have to get involved. If I were to form a new place of discourse due to being banned, it would most likely become an echo chamber of other people that have been banned not a major place of discourse.
What's wrong with that? If you hold bad opinions that most people dislike, you're not guaranteed an audience. If you have white nationalist opinions, the rest of us don't have to be held hostage to your views.
Unless they are harassing you about it (in which case first step is to block them), I don't see how this is a problem.
Does being aware of other's opinions and/or reading about them hurt you somehow?