The general sequence, from a missed payment to something serious
The first consequence of missing a property tax payment is almost always interest and penalty charges added by the municipality, compounding the amount owed the longer it goes unpaid. Municipalities generally send notices as arrears build, and there's typically real time and multiple points of contact before anything more serious happens — this isn't usually a fast or silent process.
If taxes remain unpaid for a long enough period, Ontario municipalities have the legal ability to register the property for a tax sale, a formal process with its own notice requirements and timelines set out in provincial legislation. Reaching that stage generally takes years of unpaid taxes, not months — but interest accumulates the entire time, which is what makes acting early worth far more than waiting.
Why acting early is worth so much more than waiting
Municipalities are generally more willing to work out a payment arrangement early in the arrears process than after it's escalated — a phone call to the municipal tax office, made before things get serious, is almost always the cheapest and least stressful path forward.
For an owner whose situation isn't improving, selling the house — whether listed or sold as-is for cash — before arrears grow further is often the option that protects the most equity, since interest and penalties keep compounding on unpaid taxes regardless of what else is happening with the property.