Whenever a client of mine wants to omit someone who might be seen as a logical beneficiary, such as one of his or children or a spouse, I always recommend that a line or two of explanation be included right in the will. The words regarding a child are usually along the lines that the parent had given one particular child a lot of financial help that the others didn't receive, and therefore the parent would leave that child less (or nothing) so that all the children ended up being treated equally.
With respect to a spouse, the explanation might say that the spouse is financially independent from the deceased, or that the deceased left assets outside the will such as a life insurance policy.
Including an explanatory clause like this can go a long way to soothing hurt feelings. People tend to be upset when they are treated differently than the other kids under a will. They tend to ask, "what did I do wrong that caused me to be left out?" If there was an explanation such as the one I suggested above, they will see that they weren't actually left out at all.
In all jurisdictions in Canada, spouses have the right to contest a will if they are not adequately provided for by their deceased spouse's estate. Having a clause that explains that life insurance policies or pensions or RRSPs were left directly to the surviving spouse provide evidence that the spouse has been looked after financially. The clause can help end or even prevent a challenge to the will.
Why let your beneficiaries think you spited them on purpose, causing them to launch a challenge against your will, when you can keep everyone happy with a few words of explanation?
Cartoon from www.andertoons.com