Originally Posted by Goldorak

With 8 hrs, you have indeed time to see something, but certainly not to "explore". If I were you, I would take the train from CDG to St Michel-Notre Dame and walk around this area. From the Pont Neuf, you can take a boat tour on the Seine (a must-do). Schedule ample time to return to CDG (leave St Michel about 3.5 hrs before your flight to YYZ). You can buy your return ticket in CDG, so you will save time not having to deal with this at St Michel.