Short layover in Toronto flying from US to Paris .

This is from a passenger and former passenger services agent perspective:

if you miss the connection and it is Air Canada's fault they will just arrange to put you on another flight, maybe even while you are still airborne. Or if the flight leaving out of Cincinnati is going to leave late Air Canada would probably advise you not to take the flight as you would not make the connection and re-arrange things for you.

Could you book inexpensively an early one way to Toronto separately
$400 is a big difference.

Figure out what's the worst that can happen if you miss your connection (going there), as in when is the next available flight. A $400 difference is not peanuts (I wouldn't likely pay it), but it depends how much you need to make your connection and if you're Ok if you are put on a later flight.

At least you will be able to tell all your friends and family that you were, for a short while, at the centre of the universe!

In 2015 I had a connecting flight in Toronto from United to Air Canada with about the same connection time and barely made it. I don't remember the landing gate or departure gate, but it was a very long walk (run) through the airport to the departure gate via the required route. Although I was told ahead of time (by the airline) I would not go through customs, I did have to (with line wait, questions, and even had to show my previous boarding pass). Then had to go through security. My arriving flight was not late. It just took that long without any particular issues. The plane was about half boarded when I got to the gate.

I don't remember if there was any ongoing construction going on at that time that could have affected the routine.

We did this last year going RDU-MKP & return. Great, easy to navigate airport. we had longer layovers each way, however, the world-class Indian restaurant going and the abilty to bring my Grappa back in the sealed duty free bag were both great perks, along with an under $700 RT!

FYI, on the return trip you will go through US border procedures in Toronto. It's an efficient process but having two hours will make it more comfortable. I'd risk the outward-bound trip, especially if it is a fairly early flight. You will encounter security checks but probably not Canadian immigration. If the first flight is running late, inform airline staff of your connection.

Things I have learned about short connections.
1. Assume your checked luggage will not make the connection. Take what you need for the first 48 hours in your carryon.
2. Make sure you have both your boarding passes when check in in Cincinnati.
3. Make sure your checked bag is tagged to Paris and that the agent adds a "short-connection" tag too.
4. Tell your flight crew that you have a very short connection in Toronto. They may be able to expedite your exit and possibly even your trek through the airport. They may also be able to find out your departure gate before you land.
5. Find out if you arrive and leave from the same terminal in Toronto and what the route is through the airport.

I have done it, both at Toronto and Montreal coming from Denver. But it was rushed and if anything had gone wrong I would have missed it. If you can do this at a similar price with a longer layover, why not?

The US terminal, because of the pre clearance for US immigration, is a completely separate terminal at both airports, and you cannot cross between the two without clearing Canadian or US immigration also. My flights always seem to arrive/depart at the gates furthest from the immigration checkpoint and that means a very long walk.

Tried talking to flight attendants about the tight connection and they were willing to allow me to exit the plane as soon as the door was opened. But another passenger had other ideas about that and threatened to punch me if I tried to walk past him to get off the plane. Last I saw him he was still on the jetway talking to police. I did make my connection.