Working Permit in Canada but working for USA

[yula]

Hi, I currently have a working permit here in Canada valid until 2012 that allow me to work only for my employer.
My question is. Can I do freelance work for the USA and receive the money here. Would this be a problem when paying my taxes next year.

I see that my working permit only allow me to work for my currently company inside Canada... just want to make sure I can work for a foreign company as a self employer.

Thanks.