The rental car should have an insurance card in the glove compartment along with registration and that is what you should show. The Citi Prestige coverage is for damage to the car which means you can decline the coverage the rental car company offers. However the police officer is going to be primarily interested in seeing that you have liability coverage which is something else entirely. The car should come with basic coverage--as documented by the card in the glove compartment--for liability as required by the province in which you are driving. That should satisfy the immediate requirements of the police although it may or may not be sufficient to meet your personal needs--and you may want to carry an additional liability policy for a higher amount.

Note that the legal minimum required amount of liability insurance in Canadian provinces tends to be much higher than the corresponding limits in US states.