Yup, its too general, maybe Tk::Canvas::MouseDraw? MouseTrap? MouseRecord?

Is this functionality useful enough to submit to CPAN?

Sure

Do the "styles" of drawing allowed (eg. "free", "line", "oval", "circle", "rectangle") cover enough of the most commonly required drawing methods?

Its a good start, but since Canvas doesn't have too many types you should include them all :)