CPP Death Benefit made out to Estate. (Beneficiaries have high tax bracket.) This is the only amount on the T3. What tax % do I use to calculate tax owing?

As we do not support the preparation of T3 Trust Tax Returns, we are unable to advise you on this matter. Please see the CRA Guide on preparing these types of returns: https://www.canada.ca/en/revenue-agency/services/forms-publications/publications/t4013/t3-trust-guide-2016.html