1) How can African governments and private sector actors mitigate the impact of USAID funding cuts?
They can't to my mind. They need to make everything very transparent to make USAID sure that funds will be used wisely and not by corrupts.
2) What alternative sources of funding should African nations explore to sustain development efforts?
EuropeAID is an alternative but I don't know if the EU gives funds to countries that aren't in the Europe continent. Another alternative is Bank Of Asia but I'm not sure again if they give money to Africa. Btw their alternatives will be the World Bank, UNDP and private foundations.
3) In what ways can regional cooperation help reduce dependence on external aid?
They can reduce it by investing in education. Corruption kills everything, they need to lessen corruption and invest money in education, help young and educated people to study abroad and use the knowledge to improve their country.