In case of disaster it's always important to take careful note of where the actual Home Position is recorded. If you take off from the canoe it marks that spot as the Home Position, but if you then move the canoe, you need to be aware of where it'll go in the event RTH is triggered. But that doesn't mean you can't cancel the RTH function if it's triggered.Make sure your home point is set to a dry location.
Even if the canoe has moved, you can periodically update the Home Position to the current location of your transmitter, or you can drag the location of the Home Position to any chosen new location on the map (i.e. the nearest island). You can even change the Home location while the drone is already en-route during a RTH. But those options assume you still have a functioning control signal, unless you've dropped your transmitter overboard.
Hand launching isn't difficult. Catching is the challenge. It can be tricky if the canoe is moving, i.e. drifting in a current or with the wind. If you have both hands on the controller's joysticks, you won't be able to handle a paddle at the same time. Position the drone downwind from you and let it sit there in a hover at a safe height (higher than face level) . Then paddle or let the canoe drift downwind under the hovering drone so you can reach up to grab it out of the air.