If I have been paying towards my CPP beyond the date on which I turned 65, do I enter "Yes (Rare)" under line 28 (CPP/QPP)?

Are you filing a Canadian tax return?

If so, here's info on Canadian CPP Contributions that may help you. 

Yes, I'm filing a Canadian tax return

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@hadam wrote:

Yes, I'm filing a Canadian tax return

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This is the TurboTax US user community website.
Go to this TurboTax Canada website for assistance with a Canadian tax return or the TurboTax Canada editions - https://turbotax.community.intuit.ca/turbotax-support/en-ca