No, you don't need a visa for this double-stop transit. CZ should well know how to handle this maneuver including how to get you through the technical stop at PEK. Don't worry about the connecting flight being after midnight. However, when you arrive at CAN, your processing will probably require you to stay at the airport, and will likely deliver you to the outbound international gate area. With this sort of layover duration and schedule, you wouldn't have time to leave airport and do anything useful anyway. However, the terminal is relatively sparse with places to eat and things to do, so try to get something fairly soon after you arrive, before things start shutting down for the evening. If you have lounge access, or if purchasing a daypass is an option, that might be worth looking into.