Just to follow up on my own post, I found this in the CIC document FW1 "Temporary Foreign Worker Guidelines":
What kind of activities are not considered to be “work”?
• An activity which does not really ‘take away' from opportunities for Canadians or permanent residents to gain employment or experience in the workplace is not “work” for the purposes of the definition.
This is followed up by
Examples of activities for which a person would not normally be remunerated or which would not compete directly with Canadian citizens or Permanent Residents in the Canadian labour market and which would normally be part-time or incidental to the reason that the person is in Canada include, but are not limited to:
• long distance (by telephone or internet) work done by a temporary resident whose employer is outside Canada and who is remunerated from outside Canada;
Cool, that answers the "what visa" question -- none!
The tax implications I'm curious about. I would assume that it works out, in the end, that my US company does business per usual though I may want to tweak my withholdings; come tax time, I would file with both the US and Canada, and then remit payment (or request refund) from the country in which I was a "tax resident" (>183 days, significant ties), and pay the difference (if any) to the other contracting state. Obviously it'd be wise of me to hire an accountant specializing in this sort of arrangement, but the onus of taxes falls on me -- not my company... correct?
Sorry for all the questions, it's just a lot to wrap one's head around (especially if you don't speak a lick of legalese)! Just trying to make sure I've got all my i's dotted and t's crossed for when I present my case to my company.