Can they make me sign a confidentiality agreement I never had before, just to keep my job?

A new owner can certainly ask you to sign one, and unlike a non-compete, a straightforward confidentiality or non-disclosure agreement isn't banned by Ontario's Employment Standards Act, 2000 — those provisions specifically target non-compete clauses, not agreements protecting confidential business information, which remain generally enforceable subject to ordinary reasonableness limits.

Whether you're legally required to sign one just to keep your existing job is a separate question from whether it's enforceable, and it depends partly on how your continuing employment is structured — if your job is genuinely continuing rather than being offered fresh, a demand to sign new, unrelated terms as a condition of keeping the same job isn't automatically something you must accept. That said, a confidentiality agreement reasonable in scope — covering the employer's actual trade secrets, client information, and proprietary business details, without restricting where you can work afterward — is a fairly ordinary ask, and refusing a reasonable one can create friction even if you're not strictly obligated to sign it.

Read what's actually being asked of you before deciding: a genuine confidentiality clause is different from a non-compete or non-solicit dressed up in confidentiality language, and that distinction is worth having someone check.