The canoe has three huge advantages:

- it works in the absence of paths or trails
- it can carry enormous loads
- adding people to it makes it go faster

The first is probably the most important. I've paddled a distance while someone else walks (for various reasons) and if the person is walking across lawn, it's about the same, and if I'm into the wind I'm probably slower. But if the person is trying to get through a forest with no trail, or is going up a ridge and back down it even on a trail, I am faster. Most of the places I take canoes to are not reachable any other way. 

When I canoe camp, we double-trip our portages, meaning each person does the portage twice. One of these four person-trips is for the boat (and accessories like lifejackets, paddles, bailer etc) but the other three are for stuff. And a portage pack can be HEAVY - 90 pounds isn't unusual - since you only need to stagger 500m with it. One person walking alone might need to take 5 or 10 trips to carry that amount of stuff. 

Walking, since it's a parallel activity, is as slow as the slowest person. But a canoe can accommodate someone who isn't even paddling, and even a weak paddler will help the canoe go faster than if they weren't there. 

So, if you're all alone, and considering strolling down a grassy UK riverbank with no load vs taking a boat for that trip, it is possibly the same "efficiency". But if you have any cargo or passengers, or even other participants, and especially if the walking path has elevation changes or there is no path: the boat wins.

Some numbers: [in Quetico and the BWCA folks average 3 miles an hour][1], keeping in mind that time is lost to portaging, checking out a cool waterfall, stopping to take pictures, eating lunch etc, suggesting that the times when the canoe moves forward it is more than 3 mph. [Another article about kayaking][2] says 3-4 miles per hour and compares it to hiking in both speed and how much of it you can do in a day. Just remember that you can't walk 3 mph carrying 90 pounds through trackless bush :-)


  [1]: https://www.boundarywatersblog.com/how-far-can-you-paddle-in-a-day/
  [2]: https://kayakingventure.com/how-to-plan-a-long-distance-kayaking-trip/