Hi
The route Turku-Tampere-Jyväskylä-Varkaus-Joensuu is a "smaller" road (tarmac, yes!!) = maybe not so much traffic and you don't necesserily need to go the citycentres Tampere and Jyväskylä. One special children-activity place on that route comes to mind, the amusement park Särkänniemi in Tampere,
http://www.sarkanniemi.fi/. The roadside scenery is also changing all the way so it's not boring to drive that way. Lots on little villages and places to take a little break on that route.
Maybe more hills than on the other route, but mostly there is crawlinglanes for "heavy traffic".
Turku-Helsinki-Lahti-Mikkeli-Varkaus-Joensuu...There is motorway from Turku to Salo and then from Lohja-Helsinki-(at least)Lahti(maybe Heinola), but also much more traffic, especially from Helsinki to Lahti. Weekends and holidayseason can cause
trafficjams (in Finlands scale) in the Lahti-Heinola area of the motorway, alternative route is the "old road" just beside this new motorway. This route goes almost through "the thousand lakes" area so imo the scenery is maybe better here.
I believe that there is a lot of broschyres of Finland available in the Stockholm-Turku ship, so with a map and those broschyres you can check the details of various places.
Tourist Information webpage, http://www.visitfinland.com/w5/index.nsf/(pages)/index
Here you can check the roadside cameras located all over Finland.
http://alk.tiehallinto.fi/alk/frames...rat-frame.html