Please suggest the best guide book for..
 

Lithuania, Latvia and Estonia for my cycle holiday this summer?

Take a look at the free In Your Pocket guides:

https://www.inyourpocket.com/lithuania

You should try to plan your vacation in Estonia around early July, so you can attend the song festival that is scheduled every 5 years. It is an amazing experience as the entire country comes to sing at the same time.
We enjoyed the amazing experience in 2014 in Tallin. The singing, the people and their patriotism is unforgettable.
Have fun planning, it is a great country to visit.

Thanks guys/gals. Any other books?