There has been a fair bit in the news lately about children challenging wills because they were partially or entirely disinherited. In some jurisdictions, particularly British Columbia, it is very difficult to entirely remove a child from a will because of moral obligations built into the BC Wills Variation Act. In Ontario, by contrast, it is much less difficult to do so. The Succession Law Reform Act does not require that a person leave assets to anyone; unless you can prove that you were financially dependent on the testator, you may have difficulty challenging the will simply because you were left out.
Where you live can have a fairly significant impact on your testamentary freedom. If you are seriously thinking about cutting out a child, you should speak to a lawyer to make sure you can.