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The "best" answer so far is to take a tax credit, which is cumbersome and misses the point. The U.S. does not tax these benefits, period, regardless of how much foreign tax is paid. A Canadian residence should be sufficient for TurboTax to consider the payments non-taxable on a U.S. return. Is there any place in TurboTax to specify the non-taxable portion (in this case 100%), as is done for RRSPs?
The Help for the Social Security Benefits Worksheet in the CD/Download TurboTax software says if you are a U.S. citizen residing in Canada, do not enter the amount from box 5 of your SSA-1099. It doesn't say anything about needing Form 8833. Apparently they think it's okay to just omit the income, and not show it on line 6a.
I don't think that omitting it would cause any trouble. The IRS knows it's not taxable. They don't go after people when they can see that they are not going to be able to collect any additional tax.
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