While the grand canonical partition function $Z(\mu)$ with chemical=20 potential $\mu$ explicitly breaks the $Z_3$ symmetry with the Dirac=20 determinant, the canonical partition function at fixed baryon number=20 $Z(B)$ is manifestly $Z_3$-symmetric. We compare $Z(\mu=3D0)$ and $Z(B=3D0)$ formally and by numerical simulations,=20 in particular with respect to properties of the deconfinement transition.