Firstly, what you're calling a labour monopoly is a certificate awarded by the Ontario Labour Relations Board, which certifies an employer for a unit of employees. There aren't one or two of these. There are thousands, literally tens of thousands of them. They certify grocery stores. They certify municipalities for their own employees. They certify hospitals. They certify nurses. They certify a host of people under the Labour Relations Act.
The labour monopoly does not come from the operation of the Ontario government. The Ontario government does not say you get to have a monopoly.