Can I sue a tax preparer for negligent advice that resulted in penalties in Ontario?

Yes, if the preparer's work fell below what a reasonably competent tax preparer would have done and that caused you a loss beyond the tax you legitimately owed. A common misunderstanding here is what's actually recoverable: you generally can't claim back tax you genuinely owed, since you would have had to pay it regardless of the preparer's conduct. What you can potentially recover are the additional costs the negligence actually caused - penalties, interest, and professional fees for fixing a return or handling a reassessment or objection that a competent preparer would have avoided.

A claim can also arise where the preparer failed to advise you about an available deduction, credit, or planning opportunity a reasonably competent preparer would have flagged, causing you to overpay or miss a benefit you were otherwise entitled to. As with other professional negligence claims, you'll need to show what a competent preparer would have done differently, which usually means getting another tax professional's opinion on the file. Keep your original filing records, correspondence with the preparer, and any notices from the tax authority, since they're the core evidence in these disputes.