Title Insurance or Survey?
You're right, in Ontario lenders do require title insurance to be purchased. Some, however only require lender's title insurance as the minimum requirement which means that you don't get any benefit from this insurance, only they do. Check with your lender and lawyer and if that's the case, ask if you can extend the coverage to homeowner as well.
Title insurance is an excellent product and great value for money. However, there are limits to its coverage. Title insurance ins't boundary insurance. It also doesn't prevent you from buying a house that you later regret because you didn't do your research thoroughly enough. A survey plan and a consult with a surveyor can help you uncover and understand potential boundary issues (like fences in the wrong place and neighbouring structures encroaching on your property) in the same way that the home inspection does for the house itself.
To answer your question, there is no law that states you have to have a survey plan. However, in the interest of making an informed buying decision and reducing your risk of buying a property that you later regret, acquiring a survey plan as part of your research and due diligence on a property is a great idea.