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@Charm wrote:

The previous accountant filed a resident return

  I would have filed a nonresident return which I know has income allocation scheduled. But I want to be consistent with what was filed in 2021.

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Except for certain elections, filing a 1040 (Resident Alien) versus a 1040NR (Nonresident Alien) isn't a choice - it is a matter of facts.  *IF* the prior year was incorrect, don't mimic it by filing another potentially incorrect tax return.

Is he a Resident Alien or a Nonresident Alien?  Last year was the taxpayer a Dual Status Alien?

You said he lived in and was a Resident of Canada, so at first glance the prior return may be wrong, but without seeing all of the details, it is difficult to know.