Can an Ontario estate trustee be personally liable if the Estate Administration Tax isn't paid correctly?

Yes — but through specific routes. The Act makes the tax itself payable by the trustee in a representative capacity only, out of estate assets (s. 2 (8)). Personal exposure arises when a trustee distributes the estate without paying the tax (a breach of fiduciary duty) or gives false or misleading information in the Estate Information Return, which is an offence carrying personal fines or imprisonment (s. 5.1). Ontario's Estate Information Return requires the trustee to disclose detailed asset values within a set window after the certificate is issued, and inaccurate or incomplete information can trigger a reassessment, additional tax owing, and scrutiny of the trustee personally, not just of the estate's assets.

This risk is separate from, but related to, the broader duty an estate trustee owes to administer the estate properly, distributing assets or winding things up before the estate's tax obligations, including the Estate Administration Tax and any reassessment of it, are properly sorted out can leave a trustee exposed even after the assets are gone. Genuine, good-faith estimation errors are treated differently than careless or deliberately understated values, but the trustee still bears responsibility for getting the numbers right and correcting them if they turn out to be wrong.

Because the personal exposure here is real, an estate trustee should value estate assets carefully, keep documentation supporting the values used, and get professional help completing the Estate Information Return rather than estimating alone.