No if they are not a legal adult (18 years of age or older), and no if they are a beneficiary or Attorney under either document.
Check out our brief but detailed summary of the rules for who can be a witness for a Will here: https://www.notarypro.ca/blog/who-can-witness-my-will-in-ontario/ and the rules for who can witness a Power of Attorney here: https://www.notarypro.ca/blog/who-can-witness-a-power-of-attorney-in-ontario/
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Questions? We are here to help via email: email@example.com