There is a very well-known case in Ontario called Banton v. Banton. In that case, an elderly man married a waitress in his long-term care facility and subsequently redid his will, cutting out his children from his first marriage and leaving his new wife his entire (substantial) estate. When the children challenged the will, it was found to be invalid because he had no capacity to make a new will, but because he had married, he had revoked the old will, and so his new wife still inherited a significant amount of the estate.
There is a requirement in Ontario that a person signing a will must have what is called testamentary capacity, that is, the ability to understand what he or she owns in terms of assets and who he or she owes obligations to (spouse, children, other dependants, etc.). However, there is no requirement that a person have any particular level of capacity to marry. Marriage in Ontario automatically revokes a will, and so “predatory marriages” have the potential to throw very careful estate plans into complete disarray.
Unfortunately, this situation still happens. There are many estates lawyers who believe that there should be a capacity requirement for marriage, considering how deeply it can affect an estate plan, but until this happens all we can do is be vigilant.