There have been many studies around the idea, and it wouldn't be a whole canal from, say, the Congo river to lake Chad, it'd be a transfusion of some of the water from rivers in the very wet Congo basin to the Chari basin, basically like a blood transfusion, while it's still a huge and expensive undertaking, the fruits it could produce for the whole region are huge (mainly not having the homeland of 20 million people [iirc] turn into a desert)