Excarina has a loose connection to the manga. It takes some liberties in its storytelling, but whether that's a good or bad thing depends on your perspective. Some fans appreciate the changes, while others prefer a more faithful adaptation.
Not really. There are quite a few differences between Excarina and the manga.
Overall, Excarina doesn't adhere strictly to the manga. Some characters and plotlines have been significantly altered for the adaptation. However, it still manages to capture the core themes to some extent.