If the marital status relationship has not changed during the tax year, then one of them has to claim the spousal amount even if it will not affect their tax liabilities. In this case, you will not be able to claim the eligible dependant amount.
The only time you can override this is when a break in the relationship happens. Then you get to choose between the spousal amount or eligible dependant amount.
Here is a link on when you can claim the eligible dependant amount :
https://turbotax.community.intuit.ca/community/family-education/help/who-can-claim-the-tax-credit-fo...
I hope this was helpful
