The short answer seems to be no. Donor means the person making and giving the Power of Attorney. Testamentary means – through one will or upon your death. In the Ontario case of Richardson v. New, the court held that a beneficiary designation is the same thing as a testamentary disposition. This was upheld later by the Ontario Court of Appeal. In English, one of the few restrictions upon what an attorney can do under a Power of Attorney is that they may not make a Will for the donor. The courts by calling a beneficiary designation, in essence, a testamentary act are saying that this is the same thing as making a Will. Specifically, an attorney is required under the Substitute Decisions Act to act in the best interests of the donor. Clearly changing a beneficiary designation that will only take effect after the donor’s death will have little to do with the best interests of the donor. This is very different from where the donor does have mental capacity but does not have the physical ability to make the beneficiary change requested. In those circumstances, someone changing a beneficiary designation is simply acting as an agent and clearly does have the authority to change a beneficiary designation under those very limited factual circumstances.
This situation was discussed in the Hanson Estate, a decision of the Ontario Superior Court of Justice which held that the Substitute Decisions Act was not involved at all and that it was simply an act by an agent and as such was perfectly acceptable.