Is it mandatory I use an Agent in Canada to schedule an itinerary?
No, absolutely and definitely not.
Canadian immigration is very clear that nothing about applying for a visa needs to be done by an agent. Everything can be done by the person making the application. In fact Canadian Immigration actively warns about false information being put about by unscrupulous agents claiming that an agent was necessary for some things.
With regard to the itinerary, all that is needed is a description of roughly what you intend to be doing and where in Canada you are going. It does not have to include booked tickets or hotels. It certainly does not have to be created by a travel agent. Immigration understand that most people wait until they have a visa before booking things.