Affidavit
A written statement sworn under oath or solemnly affirmed before a commissioner, typically for court proceedings, estate filings and OSAP. It ends with a formal jurat naming the commissioner and the place and date.
Statutory declaration
A solemn declaration made under the Canada Evidence Act (or Ontario Evidence Act) where a court affidavit is not required — common for government departments, common-law unions, insurance claims and lost documents.
What they share
Both are made in front of an authorized commissioner, both carry the same penalty for making a false statement, and in most cases you must sign in the commissioner’s presence — not in advance.