I've had to fill in a W8BEN for my investment account in Canada (it would potentially allow me to buy US-located assets). And keep in mind that the vast majori

I've had to fill in a W8BEN for my investment account in Canada (it would potentially allow me to buy US-located assets). And keep in mind that the vast majority of countries have tax treaties with the US such that you'll get tax credits for foreign taxes paid. You'd only pay taxes in both countries if you're living somewhere with lower taxes than the US.