When you have decided whether you intend to start from Greece or Italy, let us know.
Someone will then (maybe) be able to tell you which (preferably scenic twisty, non-motorway) roads to ride all the way to Calais in July.
When giving your jump off point, it would be great, mate, if you could also let them know:
1. How many days you have available to travel between Greece / Italy and the north east French port
2. Whether you want to ride: 50, 100, 200 or 300 or more (or less) miles a day, down these twisty scenic (non-motorway) roads.
3. Some basic guidance as to whether you are a 'Get cracking at dawn and ride 'til dusk' merchant or more of a '11 AM start, no later than 15:30 finish, showered, beer in hand, chilling' fellow, would be handy, too.
4. What sort of hotels / campsites / B&B you (might) have in mind to overnight in. In short, are you a 'Wild camping / put it up in a car park' fellow? Or more of a 'I expect someone to carry my bags, turn down the sheets and put an arrow fold in the toilet roll after each visit to the porcelain', sort of chap?
From a very quick look, Salerno to Calais direct is roughly 1000 miles, whilst Lavrio (no 's' at the end) appears to be nearly twice as far at 1800 miles. This 80% increase in the distance highlights the importance of giving the number of days available between points A and B to make the journey. If it's two days, you might need to get your skates on. If it's two weeks or two months? Well that's a whole different ball game.
Await your news with no little interest.