Browsing around public-domain comic books led me to Supermouse #5, and https://comicbookplus.com/?dlid=79085 page 12, a story with a rabbit whose name I could not find and Roscoe Mouse. So here's a copy of their pose in the title panel for this. No, Roscoe is not Supermouse, although he seems to be some relation. Possibly a nephew or something. References from the original but not traced, as my rabbit's much more round hips indicate.

Doing something for the circus poster lettering was challenging.

Comic book original art by Milt Stein, figures ComicBookPlus.com.