American working in US and Canada

[poncho]

Hi there, I haven't been able to find this specific situation on your forum. It might be my searching ability so I apologize if you've seen it before.

I live in the US and am a citizen here. I used to live in Canada and so I guess I'm still a citizen there although I haven't lived there in many years. I am employed in the US and pay my taxes in the US.

I am being offered an additional job in Canada that I would do part time as a telecommuting employee of a large corporation in Ontario. I'll visit sometimes, but 80% of the time I'll be based in the US. This corporation wants to pay me as one of their regular Canadian employees and I suspect there will be automatic deductions for Canadian taxes.

Do I have to pay taxes in both countries? In one country? Can I stop them from deducting taxes automatically? What IRS forms should I be looking for and does any mainstream tax program like Turbotax have these forms?

Thanks in advance for any assistance!