No. Under Ontario law there is no requirement that, in order to be valid, a separation agreement must be notarized. In fact, there are surprisingly few legal requirements in connection with creating a valid separation agreement, namely: 1) it must be in writing, and 2) it must be signed by both parties and witnessed by someone aged 18 years or older. It should also be dated.
There is no requirement that the needed witness to the signing of the agreement must be a lawyer, a Commissioner for Taking Oaths, or a Notary Public.
Note that “notarizing” a separation agreement is not the same as getting Independent Legal Advice (ILA) from a lawyer experienced in Family Law issues. We strongly recommend that each party to a separation agreement obtains ILA before signing.