Is there any way to inexpensively get a visa to work in the US for 4 months as a Canadian?
In short, no. Typically, if you opted into a co-op program with a university like UWaterloo, you would be paying (EDIT:) fees to [UWaterloo] (typically in the order of $700 per academic term) to coordinate your J-1 Visa with their sponsor, Cultural Vistas (who handles most of the work, including the main sponsorship, for you - provided that you release the correct details of your citizenship, and answer a few questions that are mandatory for any J-1 visa applicant).
If you need to do it yourself, the fees will run anywhere between $200 to $600, depending on type of Visa, length, and eligibility based on citizenship (as a Canadian, you should be OK - this is a problem for other nationalities because of the non-NAFTA-like agreements. See this link for more details about eligibility and fees, but please do more research before asking questions like this.
There is no "easy" way to do this either - typically, it takes between 3-8 weeks to obtain a J-1 visa, if you have a sponsor like CV lined up. Without a sponsor, you will not be able to obtain a Visa, and will then have to reneg on your job offer from the US company. See this for more details on program sponsors.
Please note: Somebody needs to be responsible for the SEVIS (application) fee; try e-mailing your recruiter or HR manager for more details about who will cover this, since it can be pretty hefty if you don't have any USD lying around.