As per the Canada Revenue Agency (CRA) Lump-sum benefits
If you received a lump-sum CPP or QPP payment in 2023 and parts of it were for previous years, report the whole payment amount on line 11400 of your 2023 return.
If the total of the parts that relate to previous years is $300 or more, the CRA will calculate the tax payable on those parts as if you received them in those years only if the result is better for you. The CRA will tell you the result on your notice of assessment or reassessment.
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