I'm writing this bug with my ISV hat on. I distribute libcanberra usually in a RPM or DEB, but also in a tarball. In the latter case libcanberra will look at the build-time-specified location of where it expects to find its plugins and fail since it won't be there (unless the user extracts the tarball to root, which probably negates the reason they decided to use the tarball).
My suggested solution is a new property CA_PROP_PLUGIN_PATH. Does this make sense? I can look into creating this patch myself.