TurboTax automatically claims medical expenses on the return that results in the highest net benefit to both taxpayers.
If you are preparing your return together with your spouse, you cannot split medical expenses between you. If you prepare your returns individually, you can each claim your medical expenses on your own return. Before doing this, be sure that you each have enough expenses to exceed the threshold.
In Québec, medical expenses are based on combined family income and not individual income. After the credit is calculated on the taxpayer's return, the spouse can claim any leftover non-refundable tax credits (including medical expenses) on their tax return at line 44000. In most cases, this would be most advantageous.
On the Medical Expense Claim (Québec) screen, choose which spouse will claim the medical expenses. Any leftover non-refundable credits are automatically claimed on the other return.