I don't work for Intuit, but I do have an "Ask TurboTax to answer" button. Since this is a potential programming issue, I clicked that button to get them. (Edit: I just did it again.)
It doesn't matter whether it's regular Social Security or SSDI; the point is it is *NOT* "SSI" (Supplemental Security Income) as you kept saying. SSI, a form of welfare, is never taxable. Social Security, whether regular or SSDI, *may* be taxable except for the Canadian tax treaty issue you raised. The issue is how to get TurboTax to recognize that the tax treaty applies.
