The contract used for universities is often standardized by the province. And many universities are loath to modify the contract, choosing to add an 'addendum' with additional provisions, some that in fact contradict items in the provincial boilerplate.

If you are not sent an invitation letter, I can't imagine why the university would try to hold you to a contract.

Even after you sign the contract, I would recommend that you continue evaluating other offers until you have a Z-visa in hand.