How easy is it to glide and waterland the Beaver in case of (the electric-) engine failure ?
Does that work out well , without not too many difficulties ?
Not particularly difficult. A little more judgement required than on a runway, though less worry, as you're more likely over a more suitable landing surface. It is a requirement that all planes be power off landable, the Beaver floatplane is no different, regardless of powerplant.
When I specified the motor arrangement for an electric 172 project, I specified an electric variable pitch, feathering propeller. In the case of power loss, it could autofeather, and gliding would be more easy that many piston powered airplanes.
Yes, as we found, there are penalizing performance (range) considerations for electric planes. But that's going to improve. Every great product improves with development. Ten years ago, you desk top computer might run for twenty minutes on the ten pound back up power supply. Now, a tablet will run all day, doing more work, and the whole thing is 5/16" thick, and weighs a small fraction of the back up battery unit. A battery the size of two choclate bars will start my car! We can't imagine the developments in such a needed product!