My only issue with your previous post was the double taxation statement.
US Tax Law
Citizens and residents are taxed on worldwide income and allowed a credit for foreign taxes. The US offers the foreign tax credit to mitigate the potential for double taxation.
Canada also offers a foreign tax credit to its citizens and residents for the same reason, to mitigate double taxation. Line 405 on the Canadian tax return.
People that fall into this situation are required to file both in the US and Canada, but aren't taxed double as you suggest.
The foreign tax credit does not clear the foreign taxes.
The only way Alfie would only pay Canadian taxes is if he earned under $10,000 or was in the States for 182 days or less.
When I say he is double taxed, I am not saying he has to pay 45% here and 35% there or what ever their rate is, I am saying he has to pay both American (a portion after credit) and Canadian taxes (a portion after credit).
CRA said:
Line 104 - Foreign employment income
Foreign employment income is income earned outside Canada from a foreign employer. Report this income in Canadian dollars. Use the Bank of Canada exchange rate that was in effect on the day you received the income. If the amount was paid at various times throughout the year, you can use the average annual rate.
Do not reduce your foreign income by the amount of tax the foreign country withheld. However, you may be able to claim a foreign tax credit when you calculate your federal and provincial or territorial taxes. For more information, see line 405.
IRS said:
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Resident Aliens
If you are a resident alien, the rules for filing income, estate, and gift tax returns and paying estimated tax are generally the same whether you are in the United States or abroad. Your worldwide income is subject to U.S. income tax the same way as an U.S. citizen. You are a resident alien of the United States for tax purposes if you meet either the green card test or the substantial present test for the calendar year.
Because he emigrated in the eyes of the CRA, Alfie would only be subject to American taxes.
Whether or not he has to pay the full American taxes I am unsure of. I am not aware of any tax treaties between Sweden and the US.