For medical expenses, it depends on the income levels and credits available to each spouse. Usually, the lower earner will see a bigger benefit. There is an exception to this general rule. If one spouse has enough credits to bring their tax owing to zero, the medical expenses may be wasted if this spouse claims them. For more information on medical expenses, please our TurboTax article: 3 Tips For Claiming Your Medical Expenses as a Tax Deduction.
For RRSP contributions, the spouse with the largest income should claim the deductions. For more information, please see our TurboTax article: Transferring Income and Deductions Between Partners to Lower Your Tax Burden.

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