Budget Rent A Car of Edmonton Ltd. v. University of Toronto

Link to case:

https://www.canlii.org/en/ab/abca/doc/1995/1995abca52/1995abca52.html?autocompleteStr=budget%20rent%20a%20car%20of%20edmonton%20v%20uni&autocompletePos=1

What would have Toronto originally argued to make the contract valid?

I need further clarification as to what defence Toronto would have originally used.

Thank you!