As an US citizen you can stay in Canada for 6 months as a visitor. You can look for employment.
If you want to work you need to apply for work permit
1) You would have to find an employer (who is willing to apply for labor market opinion (LMO) / HRSDC confirmation for your job, if required).
2) You get a job offer from an employer and see if it falls under North American Free Trade Agreement (NAFTA) professions list (you can check the list here:
http://www.nafta-sec-alena.org/en/view.aspx?x=343&mtpiID=147#Ap1603.D.1). NAFTA allows expedited entry. In this case the employer need not apply for LMO.
You can check this manual:
http://www.cic.gc.ca/english/resources/manuals/fw/fw01-eng.pdf, for more information.