Courts in both the U.S. and Canada find themselves in challenges brought about by people who believe they did not receive their fair share of an estate, according to The Globe and Mail in "Left out of the will? Here are your options."
The options for challenging a Will in Canada are very similar to those in the U.S. Essentially, there needs to be a good reason why the court should disregard the Will and distribute the estate differently. One of the more common reasons is undue influence. Generally speaking, undue influence is an allegation that someone has inappropriately influenced another who has diminished capacity of some sort to create a Will for the benefit of the influencer. The elements and burdens of proof regarding undue influence vary from jurisdiction to jurisdiction.
Not just anyone can challenge a Will. Only people who have an interest of some sort in the estate can make the challenge.
If you find yourself on either side of a Will challenge, an experienced probate litigation attorney can advise you of your options.
Reference: The Globe and Mail (Feb. 26, 2018) "Left out of the will? Here are your options."