Turbotax offered me the option to put in amounts paid for EI (box 18), and for Union Dues (box 44). CPP contributions (box 16) and RPP contributions (box 20) do not qualify according to the tax treaty because these payments go toward a specific economic benefit (pension payments).
Per IRS publication 514, if you get specific benefit from a payment you make, it is not a tax, and you don't get credit for paying it. So if you pay into the Canadian Pension Plan, it's possible you can retire and collect a pension, so that means you will get a specific benefit from the payment. EI is different because it is calculated on a flat percentage of salary basis, and so it qualifies as a tax. Here is the specific text that says required foreign pension contributions are not taxes and EI benefits can be considered taxes:
"A foreign tax imposed on an individual to pay for retirement, old age, death, survivor, unemployment, illness, or disability benefits, or for substantially similar purposes, is not payment for a specific economic benefit if the amount of the tax does not depend on the age, life expectancy, or similar characteristics of that individual. No deduction or credit is allowed, however, for social security taxes paid or accrued to a foreign country with which the United States has a social security agreement. For more information about these agreements, see Publication 54."
This is my best guess and the way I'm entering things, and I am noting that here for when I forget what the rules are next year. I am not a tax expert, though.
