To get a work permit, you first need a job offer.
Here are some job websites:
http://www.canadavisa.com/career_zone/canadian-immigration-job-search.htm
http://www.jobbank.gc.ca/
http://www.eluta.ca/
http://www.monster.ca/
http://www.workopolis.com/
It's not easy to get a job offer online. You can also look into if you qualify to immigrate directly, see http://www.cic.gc.ca/english/immigrate/index.asp For example if you fall under the title college and vocational instructors, see http://www5.hrsdc.gc.ca/NOC/English/NOC/2006/QuickSearch.aspx?val65=4131 , you may qualify to apply under the Federal skilled worker program, see http://www.cic.gc.ca/english/immigrate/skilled/apply-who.asp