The short answer: A consent or declaration for use in Ukraine can be signed and certified while you stay in Canada. Two routes work: certification at a Ukrainian consulate, or signing before a Canadian notary with an apostille and a certified Ukrainian translation afterwards. The main caveat: the receiving Ukrainian institution often has fixed expectations about wording and form, so the text is confirmed with that institution before you sign anything.
This usually arises around family and property moments: a child travelling, a spouse selling a jointly owned asset, a registry that wants a declared fact. The signature itself takes minutes; the surrounding work is drafting the text the Ukrainian side will accept on first submission and running it through the certification chain that fits the deadline.