In my opinion, the best way to learn the bel canto style would be listening to recordings of Gary Karr. He is famed for how he can make the bass "sing". Bel canto is the Italian operatic singing style. For me, it clicked after hearing Gary play "Elucevan Le Stelle from Tosca Arct 3". It is, after all, Gary playing the melodic vocal parts of the opera.
I believe that it takes a musical ear to learn a style. I think that marks on a paper can only go so far. If you listen to enough recordings, you will know where the emphasis of a phrase is without the help of accent marks. If you specifically want to learn the style of Bottesini, then I suggest that you buy Joel Quarrington's "Bottesini: Music for the Double Bass".
There's no better way to learn the style than listening to the style. It's the same way we all learn how to talk, it's the same way we all learn how to whistle, it's the same way we learn to be musical.