Non US citizens/residents and non Canadian residents are required to fill out and return Form W-8 BEN (proof of non US citizen identity) for exemption from Capital Gain Tax in the United States when opening an account.
The tax system in the United States covers investment products originating from the United States (whether they are tradable securities, mutual funds, or bonds), and investors, whether they are US citizens or permanent residents (also known as green card holders), are required to pay a 30% Dividend Withholding Tax on dividends as long as they hold these investment products in their personal names.
Due to the potential additional tax burden associated with overseas investment products, investors should seek tax advice based on the situation