I’ve been thinking about this a lot lately, particularly since a case a couple of months ago about a man who cut out his daughter from inheriting any portion of his estate; evidence suggests that it was because she, a black woman, had a child with a white man, and her father did not approve.
In Ontario, generally, you have testamentary freedom. This means that you can leave your estate to whomever you choose, in whatever proportion you choose, provided that you have considered anyone to whom you own an obligation, such as a spouse or a minor child. Usually, there is no obligation to leave anything to an independent adult child, as in this case. I have had clients who were estranged from children, siblings or parents for a variety of reasons and chose not to leave anything to those people; under Ontario law, there is no reason they have to. The major exception is for spouses: you cannot fully cut out a spouse in most circumstances. If you want to, you should absolutely have a domestic contract in place to back it up.
If you are considering cutting out a close family member, you can, but you should be sure to have your will done by a professional.