The length of time will be indicated in your passport at the time you enter Canada. It cannot exceed the expiry date of your passport. You will find lot of information with a Google "length temporary work permit canada". The following has lots of information and includes extending your WP. TRV must also be extended if you are not from a visa exempt country.
http://www.cic.gc.ca/english/information/applications/guides/5553ETOC.asp
