Is the area around Dunkirk and Calais, including the cities, suitable for bicycle tourism in July?
My concern is that, being two not-so-small ports, both can offer nothing more than long lines of trucks and industrial areas.
I'd do it.
I assume near the ports and in the case of Calais, near the Eurotunnel complex there will be more trucks and non bike friendly roads highways and access ways.
In the city proper, I expect it to be like any other towns with some not always connected bike paths.
It looks like if you get out of the towns, you will quickly be in the coutry side with more bike friendly roads.
Have a look at this (one site among many) :