Can my Executor also be a beneficiary in my Will?

Yes. In fact it is very common to name one's spouse as the Executor and the main beneficiary of the estate. There are certain advantages to doing this.
Your Executor is responsible for gathering up the assets in the estate and distributing them according to the instructions in the Will. If your Executor is also the main beneficiary, then they probably have good insight into the extent of your assets, and are likely to have good access to the assets at the appropriate time. Furthermore, the distribution of the assets will simply be transferring the assets into their own name.
The other advantage is that no professional Executor fees will be incurred, preserving the value of the estate for the beneficiaries. Typically a lawyer or professional Executor charges a percentage of the estate that can be as high as 3-5 percent of the total value. This means that an Executor transferring ownership of a house could pay themselves $20,000 for a few hours of work.
However, your Executor does need certain attributes to be effective. There is a great deal of administration and paperwork that has to be filed when working with an estate, and some of this work is subject to tight deadlines imposed by organizations like the Canada Revenue Agency. Your Executor must be capable enough to work through this administration, bearing in mind that your loved ones may be grieving after your passing. Your spouse may not always be the best choice of Executor because of their age or emotional state.
In summary, appointing your main beneficiary as your Executor is certainly permitted, and is very common. You would need to decide if your main beneficiary is the best choice of Executor in your own personal situation.
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