Your time is somewhat restricted 5:45 is not a lot of time. You really only have about 2:30 or 3:00 to play with. The rest of your time is taken by general airport navigation, the need to arrive at your gate before the scheduled departure time, clearing security if you've left the clean zone, and a buffer for safety.
YYZ is about 30 minutes of driving from downtown Toronto. It can be worse with traffic but you are traveling on a weekend so I will assume that will not pose a problem (not a guarantee).
Your itinerary (YVR-YYZ-CDG) suggests your bags will likely be checked through unless you are switchling between airlines that are not interlined and you will be checked-in with a boarding pass in YVR. Given some of your passengers are flying J you are probably flying Air Canada out of Terminal 1 (WestJet has no J class).
To my knowledge, there is no place to store carry on luggage at YYZ due to security concerns though I must confess it is not something I have ever had to do so.
If you do choose to go downtown to see the CN Tower you will need to rent a car or hire a cab. Both are somewhat costly. You could, in theory, drive downtown and see the CN Tower for about two hours then come back to the airport.
A more realistic and more relaxing recommendation is to enjoy the Maple Leaf Lounge / the applicable loung of the carrier on which you are flying. You should be able to purchase passes for those not entitled to enter.