Are you sure you need to replace the canister and vent control valve? Do you have specific trouble code? Trouble codes associated with those components are sometimes jut due to loose connections/fittings or cracked tubes. Jack up the car and make a thorough inspection of tubings and fittings. If you have to disconnect tubings, make sure you mark them as it can get complicated if you make a mistake.
EVAP related CELIt could even be caused by a defective or ill-fitting gas cap or corrosion on the area.
For reference, look for trouble codes P04xx in the link below:
http://www.nicoclub.com/FSM/i35/2002/ec.pdf