Executors should be paid a fee for services performed since, as you know from personal experience, there can be a fair amount of work involved in settling the estate. The will might state a fee (e.g. 1% of the estate) but, if not, the probate court can decide what the fee should be and authorize the executor to deduct the fee from the assets of the estate before distributing the assets, filing the final income tax return and estate tax return, etc. The court also might choose to decide that an executor's fee stated in a will is too small or too large and change it.
Whether Canadian law allows a beneficiary to be the executor as well is something
you need to find out from your own lawyer. In the US, laws regarding inheritance
also vary (usually in definitions of terms, and many details) from state to state, and if
a similar situation occurs in Canada too, then your lawyer will tailor your will
to the laws of your Province. But, please understand that will-making is really
not a do-it-yourself
process, and I urge you to have a lawyer draft the will rather than relying on advice
from Internet forums -- including this one!
Squabbles between beneficiaries, one of whom is the executor, are not unknown. But
beneficiaries have also been known to sue a non-beneficiary executor, or move the
probate court to dismiss the executor etc because the beneficiaries are unhappy with
the way the estate is being divided among them by the executor. If you trust
your sister and the laws of your Province allow it, by all means consider having
her be the executor of your will. But be aware that if you are passing over
your spouse or adult children in naming your sister as executor, there
are going to be hard feelings.