2.5 hrs too short for a transit? Not usually. You will need to clear exit immigration at PEK and the queues are variable but with more than 2 hours and an intime arrival you should be fine.
But what time of day is it? The biggest peril is Air Traffic delays which generally build up during the day and internal flights within China get affected the worst usually. So if your CAN PEK sector gets delayed, what are the potential plan B flights to get rebooked onto to get you to CDG. Is your time of arrival in CDG critical? If it is, a direct flight out of CAN might be a better option...