The only difference if his family lives in Canada or Mexico, is that he can claim his child as a dependent if he files a joint return with his wife, even if his child did not move to the US during 2020.
The taxpayer still can’t claim his child as a dependent if he files as married filing separately, because the child did not live with him for more than half the year. And the rules about filing jointly with his wife only if his wife is a US resident or if he makes the election to treat his wife as a resident, and the rule about paying US tax for all his wife’s worldwide income if they file jointly, still apply.
