If you look at subclause 12(4), the provision that creates a deemed overpayment of tax, you see that the Canada workers benefit is a refundable tax credit. The mechanism for providing refundable tax credits is that you have a deemed overpayment of tax. You're deemed to have paid too much tax. Once you've paid too much tax, the Canada Revenue Agency gives you a cheque, or pays you the amount of excess tax you're deemed to have paid. That's the mechanism for how these refundable credits work.
It provides that an eligible individual who files a return of income—so you have to have filed an eligible return of income and be otherwise eligible—is deemed to have paid at the end of the taxation year an amount equal to the total of...and then it's the amount for determining the amount of Canada workers benefit you get.
If you qualify, if you're an eligible individual and you filed your tax return, then you're deemed to have paid this extra tax and you just get the credit. There's no discretion built into it there. If you meet the conditions to apply, you're deemed to have overpaid tax and you're entitled to the credit.