My brother is living near Canada/USA border. He needs to live in Canada for another 5 years in order to collect Old Age Security benefits from Canada. If he lives in Canada and commutes across the border to work for a USA employer (or remotely works for an employer in the USA), to which country does he have to pay income tax to? Can he choose which country he pays tax to?
If he lives in Canada and works in US, he pays taxes to both, but receives a credit for any taxes paid to the US on his Canadian tax return so there is no double taxation of the same income.
If he lives and works in Canada for a US employer, he pays taxes to Canada only and should provide a W-8BEN to the US employer.