Some aboriginals in Canada that are under the right the circumstances exempt from Canadian taxation may nevertheless be US persons.
The IRS has made a clear statement with regard to the tax exempt status of Native Americans:
This revenue ruling emphasizes to taxpayers, promoters, and return preparers that there is no right to exemption from federal income tax for Native Americans under an unspecified “Native American Treaty.” Any return position based on an unspecified “Native American Treaty” has no merit and is frivolous. As a general rule, Native Americans are subject to federal income tax just like every other American.
This would mean that any claim to tax exemption on the basis of Canadian tax law would also be frivolous. Now it may be interesting to cite Article 25 of the Canadian Charts of Rights and Freedoms: