The maximum write off at 100% for a lease is $750 month plus HST.. If you own or finance the vehicle through bank etc it really works out to about the same.. Gas, repairs etc are also deductable. you will need a form (can't remember the number) from your employer saying you are elidgable
here is a link with some info as well.
http://www.carlogcanada.com/resources-canada.html