A pal and I did Lon2Par on our own, as a little challenge for my 50th (almost 10 years ago, mind).
Essentially followed Avenue Verte - see
this awesome planning site!
A nice leisurely 3-5 day ride. Tougher cyclists might do it in 1 or 2: we took 3½
London to Newhaven was not overly exciting....we set off on a Sunday from Tower Bridge, planned to use back roads then just decided to get out of the city as fast as we could!
Stayed with pals near the ferry, then hopped over on the 4hr ferry and had a 4 hour pedal from Dieppe -
very easy, mostly an unused train line..
Third day was longer (70m) and a little more hilly, but simply beautiful - French backroads are fabulous for cycling, & the locals understand about cyclists.
Our last morning was in absolutely pouring rain.....Paris was okay for cycling through, although I recall sliding a little down one steepish cobblestone road! VERY wet, but nice to end at la Tour Eiffel!
The hotel experience in Paris was suboptimal.....had our room "broken into" when we nipped out for a couple of hours for dinner: definitely an inside job (someone on reception pretty well inadvertently said as much). Daughters camera and some money stolen. Got the Hotel to pay up eventually 🙄
BUT....the first multi-day cycling adventure I had ever done.
In summary: go for it!!