Hello guys!
I must agree with Kuna_01. The most beautiful place to drive through is
canyon of Neretva. I suppose you will mostly include highways,
Doboj - Banja Luka - Gradiska and
Sarajevo - Zenica. Beside highways the most important road through Bosnia and Herzegovina which is highly used by truckers is
"AVNOJ" road, Sarajevo - Bihac. This road is still the best even though it has been made during Yugoslavia shortly after WW2. All other roads are less important, I'd say optional. I'm from Banja Luka so I'll show you which parts are most important for that area.
Definitely highway
Banja Luka - Gradiska. Next... The most beautiful road in this part of the country is road
Banja Luka - Jajce which actually connects Banja Luka with "AVNOJ" road.
Here starts
canyon "Tijesno" =
https://youtu.be/64YeYjbI2a0?t=640
This road is really challenging and dangerous for truckers which you can see on this video =
https://www.youtube.com/watch?v=gSHr1RnFqqU

This part is called
"Dabrac" hill =
https://youtu.be/64YeYjbI2a0?t=1640 and from here you can see this scenery
Alternative road which conects Banja Luka with "AVNOJ" road is road over the
"Manjaca" mountain.
The most important and the most frequent road in northern Bosnia and Hercegovina is
Banja Luka - Prijedor
There are many more interesting roads but I'm not sure if you can manage to put all this in the game. I'm not familiar with roads in eastern part of Bosnia and Hercegovina, so I can not claim anything about these roads. I can just say that two most important cities on the eastern part are
Bijeljina (NE) and
Trebinje (SE). Bijeljina has a really good geographical position. North from Bijeljina there is most used border crossing to Serbia. That's
"Raca".
Trebinje is also important because of the crossing to Montenegro. From Trebinje there are two roads to enter Montenegro, one towards Niksic and the other one towards Herceg Novi.
For me, the most beautiful city in Bosnia and Hercegovina is Trebinje, without a doubt. In the background you can see "Leotar" mountain.

Also when you approach Trebinje from Mostar (
Mostar - Trebinje) you cross
"Popovo polje", in English "Popovo field".
I think that would be it in general. Highways are must have and "AVNOJ" road. You choose other you like and you think are the best to be implemented in the game.