I was a bit slow in spotting this thread but I can confirm that the Italian made Shuttle Bike does work very well on water. Here's me on a maiden voyage.
I've been searching for a true amphibious bike for many years now, but it's a tricky compromise.
The wheeled canoes look great, and I like the idea of pedalling straight in or out via a slipway, but the bulk of the canoe hull looks tricky for public road use.
The Shuttlebike uses a standard bike, with all of the floaty bits folded away in pannier bags, so it could be safely ridden anywhere.
It takes about 15 minutes to assemble the frame and inflate the tubes, but then it makes a very stable boat.
I'm quite a heavy (fat) bloke, so I had an initial problem with fore and aft stability where the tubes tended to fold at the frame attachment points. I cured that by adding two thin marine ply "splints" to spread the load along the tubes. I's now very stable, even with my 195 kg.
The drive is via a flexible shaft from the rear wheel, so the pedals drive a propeller under the front wheel, a very clever and well engineered solution. So you could use a mid electric drive and get the advantage of the gears.
I haven't electrified it yet, but it's a distinct possibility !
