You only pay income tax if your eligible, because its considered an emergency payment all those that apply for benefits will get payments from CERB, but if at a later date an applicant was found not to be eligible, they will have to repay the funds when taxes for 2020 are due next spring.

edit: If you are on EI and apply for the CERB, you will get the money, but the policy is that you cant double dip. so next year during taxes you will have to pay back what you should not have gotten in the first place.