Selecting "Rivers" shows an awful lot of dry gulches and alluvial fans that haven't had water in them in half a century or more.
Navigable by canoe leaves Australia with about 50 km of two rivers in Gippsland to be navigable.
It shows the Hunter and the Nepean as a single system.
Connectivity between ephemeral waterways which are joined by ephemeral lakes is poor.
All in all I think it speaks to the ownership of the market by private interests and the lack of utility of water navigation for most people.
They used to have a few large riverboats that used to bring people from Sacramento to the bay. One called the Delta Queen and the other called the Delta King. Three presidents even rode on them including Herbert Hoover, Harry Truman, and Jimmy Carter. They permanently affixed the Delta King on the docks in Old Sacramento where you can still eat at a restaurant or stay in an onboard hotel.
https://en.m.wikipedia.org/wiki/Delta_King
All that to say, plenty of boats in and around the Central Valley.
The data is 100% from OpenStreetMap. That map only looks at things with the `canoe` tag in OSM. There are a lot of waterways in OSM which do not have this tag. If you know of missing data, you can just edit OSM and it'll show up on WWM.org tomorrow!
(I made WaterwayMap.org)
None of it's really reasonable for a binary database.
Growing up near the Mokulumne, one day I'd like to go from Camanche to the sea. It's not that far but would still have at least one portage at Woodbridge
It really depends on the watersheds. You can get to Boston from pretty far north but you would have to cheat by going down the coast from the mouth of the Merrimack River which I think captures all the rivers in southern NH/northern MA.
Regarding Boston, the interesting thing is that it used to be connected to the Merrimack via the Middlesex Canal. My understanding is that this is silted up now (which you presumably already know) but it shows how many more connections we used to have.
Not sure you can do the equivalent further south but it looks like you could do a lot of it that way--at least in theory.
I've thought of doing this, I wonder if there are any good resources on best paths to take.