Ethiopia
ethiopia
http://www.mtsobek.com/
South africa
South africa has fantastic rivers, so you'll be spoiled for choice. the most popular - for good reason - is the orange, which forms the country's northern border with namibia.
http://www.safrica.info/plan_trip/holiday/roughing_it/canoeing.htm
Uganda
uganda
http://www.adrift.co.uk/uganda.html
Zambia
zambia
http://www.zambiatourism.com/travel/listings/adventur.htm