1. Define segments: I use Google Maps to generate a rough draft for the entire trip and then search for campgrounds or alternative options WRT spending the night, water supply, markets etc.
2. Generate segments: From overnight x to overnight x+1. First with gMaps to get an idea of the distance, then on
bRouter to get a more detailed profile
3. Send the GPX file to my phone. Final edit (remove TBT coursepoints and add critical waypoints), then push to my navigation device (Garmin Enduro).
Now, the question was fairly vague.
Step 1 can take quite a bit of time and effort in order to identify and locate POIs. I personally feel that nothing beats gMaps because of the search function, among other things. I also use several other touring resources (ex: Lonely Planet, Michelin) to flag interesting destinations and exclude others that will be overcrowded.
Step 2 (essentially making sure that a day's route is of reasonable length/difficulty) can also require more time depending on the type of touring. If following an ACA or Eurovelo route, typically a no brainer. If "custom", it depends on the type of terrain and is sometimes impossible to assess properly -- in these cases, alternative fallback plans are useful.
Step 3 -- I like to be able to design a route offline on my phone, which is why I use Locus Pro (with the relevant offline maps and bRouter routing dBase). I then push the final route to my watch, attached to the stem -- probably the most efficient nav system