I absolutely love cycling and thus have quite some experience.
In Flanders and Holland a convenient way of cycling is through 'knooppunten'. A circuit of nods created to indicate great cycling roads.
There are good maps available but for touring they might be too detailed and you would end up with a big pile of maps but no worries the internet can help you. http://www.fietsnet.be/routeplanner/default.aspx
this is an online version of the map using google maps.
It has most of these 'nods' in a database and by clicking them you can create your itinerary...
You just write down the numbers you want to follow and then you just follow the rectangular signs. You will pass through wonderfull roads.
There are also long distance cycling paths marked with LF (landelijke fietsroute or in English: countrystyle cycling route), these can be found on http://www.routeyou.com/group/view/1508/lf-routes.nl
However I prefer a custom made route with the nods...
Another page to view these is for Holland: http://www.landelijkefietsroutes.nl/routes/
and for Flanders: http://www.groteroutepaden.be/grlf/v1.nsf/_/0CE90AAFD41CDC58C12571DC0040B3B7?opendocument
but this is only in dutch as far as I know...
If you want any more information about this, you can always contact me: I have all the maps and know almost all of their routes...
cheers and good luck!