US citizen doing short term contract work in Canada

I was hired by a contractor to install networking equipment at a large retail chain. I am being hired to do the installs mainly in the Midwest USA but they have a few stores in Canada that they want me to cover as well. Is there any sort of work permit or legal paper work I need to file in order to do this work in Canada? I would be working at locations in Winnipeg (Manitoba) and Thunder bay (Ontario).

Thanks in advance.

Brian

If you are not an employee, and are doing more than advising, then they should prepare paperwork that allows you to enter at their direction and work. Or a dispute may arise about your ability to be there legally on that project and work. It is a grey area sometimes as to IT smaller projects...