Do Ontario corporations still use par value shares?

No. Par value shares were abolished under the Ontario Business Corporations Act and its predecessors, and all shares incorporated under the OBCA are without par value. This is the modern standard across Canadian corporate legislation.

Under the old par value system, shares were assigned a nominal dollar amount (the "par value") that set a floor on the issue price and determined how amounts were allocated to capital accounts. The system was criticized as creating more confusion than clarity, since par value bore no necessary relationship to actual market value or fair value.

Today, when a corporation issues shares, the consideration received is credited to a "stated capital account" maintained for that class of shares. The stated capital is used for purposes such as the solvency test on share repurchases (a corporation generally cannot reduce its stated capital below the point where its assets would be insufficient to cover its liabilities) and certain other corporate financial calculations under the OBCA.

If you are looking at documentation for a very old Ontario corporation, you might encounter references to par value from a previous share structure, but any corporation incorporated or continued under the current OBCA issues shares without par value. A corporate lawyer can help you understand any legacy share structures you may have inherited.