I have do a lot of reading on US tax
when my merchant ask me to send in a W8. Although the form are still confusing me, but what I know now is.
1. I am a Nonresident Alien.
2. Nonresident alien is only applicable to income source in US.
3. The definition of source is define as where you physically generate that income. In your case
your source in Canada and not US.
AND conclusion, you are not reliable for US tax. Instead, you are realiable for tax in Canada! Pay you tax there.
But who knows, US goverment can always come out with new tax rules that surprise us. Then it end up we will need to pay 30% withholding tax! Hopefully that won't be such a day.