There is talk about pumping sea water into the Saharan desert in certain parts, which gets at that.
Also - there are lots of un-earthed treasures to be found under the saharan which was once a lush environ and have been covered with sand - so prior to flooding it, we need to lidar and excavate it.
What if we vaccuumed up all the sand and built a new island/continent with the material and just revealed everything underneath - then flooded it. (I believe UAE is in the market for more sand-built-land-masses)
I'm sure someone has done the math to figure out what the proper length is for such a canal, to avoid problems with scaling. And if you've ever been near an ocean for much time, you know the salt tends to get around. So I'm not sure how in a multi-year project you keep that to a minimum.