Does a separation agreement have to be witnessed in New Brunswick?

This answer covers the law of New Brunswick.

Yes. In New Brunswick, a separation agreement is a domestic contract, and the Marital Property Act requires it, and any change to it or cancellation of it, to be in writing, signed by the parties to be bound, and witnessed.

That witnessing rule does not on its own make a lawyer mandatory. Independent legal advice still matters, because the Court may disregard a provision of a domestic contract if a spouse signed without legal advice from a person independent of the other spouse's advisor and applying the provision would be inequitable in all the circumstances. Different rules apply to a minor with capacity to marry, who needs Court approval, and to a mentally incompetent person, whose committee or the Public Trustee may sign with Court approval.

A valid, signed and witnessed agreement on property generally prevails over a conflicting provision of the Act, which is why it is generally binding. A support provision can still be set aside by the Court if it results in unconscionable circumstances. You can draft it yourselves, but a lawyer can confirm that the wording and signing steps will hold up for your situation.