Try to get 2 recumbent cycles identical, (driver and passenger seats), frame them together considering the width of bike lanes and bike ways, link steering and rear drives, build a frame with tabs to hold hull panels, to make it into a boat shape, try to pedal / push it up some hills or inclines, alone, with just some camping gear and a week's supply of food and water in it.
Then if still keen, finalise sealing the hull part however you can; think about a pedal driven propeller out the back, you won't want to be changing to paddle tyres for every river crossing; add sealed buoyancy; see if it floats, and if you can support your payload - batteries, solar panels, generator, water, food, camping gear, spares and tools, flywheels, 2 people, etc. while not being swamped by boat wakes. Take it for a short paddle, then see if you can get up a ramp or a beach. You may want to give up by then.
Do some extensive internet searches. Bikes and pedal cars, and tinkerers, have been around for a long time, so there would have to have been several attempts at your idea beforehand.
Or just buy an old Volkswagen Beetle and make it float, as many have done before. Or look up 'Alligator', right here.
I thought of a pushbike with huge panniers, which connect to make a raft, then put the bike and gear on, and paddle it or sail it across water, re-assemble on the other side, and ride off. Simple. The weight on a small bike would be a pain, the panniers' volume would catch the wind, and everything would corrode; I didn't do it. It's fun to imagine, and play, but it's annoying when weeks or months of work leads to a waste of time and a heap of junk; I've done it myself. Have fun, but quit if having nightmares.