Can CRA place a lien on my house in Ontario to secure a tax debt?

Yes. CRA can register a certificate confirming a tax debt in Federal Court, and once registered, that certificate has the same effect as a court judgment. From there, it can be registered against real property, including a house in Ontario, creating an effective lien or claim against that property, similar to how a judgment creditor would proceed against a debtor's real estate.

What's slightly different here is the process that gets CRA to that point: rather than suing you and obtaining a judgment through a lawsuit the way a private creditor generally would, CRA can go through this administrative certificate process instead, which is generally faster and simpler for CRA than a full court action. Once the certificate is registered against your property, it can affect your ability to sell or refinance that property without addressing the underlying debt, since the claim is now tied to the property itself rather than just to you personally. If you own real property in Ontario and have a significant unresolved tax debt, understanding that this mechanism exists, and that it doesn't require a traditional lawsuit first, is an important part of assessing how exposed your property actually is.