Hi, is it possible to give a company/person the right to manage a property in Ontario?

And if the legal paper is done outside Canada, is it still effective by law?

What you are seeking is a limited power of attorney for property. This can be prepared by a lawyer and specify a person responsible for all matters related to this specific or all properties that you own.
This empowers the (agent) to collect rents, pay bills, make repairs, hire workman etc as required on your behalf.
This could be an agent directly or a property management company. Where this power of attorney is signed is moot.