  We report on a comparative study of the profile of the CKM unitarity
triangle, and the resulting CP asymmetries in B decays, in the standard model
and in several variants of the minimal supersymmetric standard model (MSSM),
characterized by a single phase in the quark flavour mixing matrix. The
supersymmetric contributions to the mass differences \Delta M_d, \Delta M_s and
to the CP-violating quantity |\epsilon| are, to an excellent approximation,
equal to each other in these theories, allowing for a particularly simple way
of implementing the resulting constraints on the elements of V_{CKM} from the
present knowledge of these quantities. Incorporating the next-to-leading-order
corrections and applying the current direct and indirect constraints on the
supersymmetric parameters, we find that the predicted ranges of \sin 2 \beta in
the standard model and in MSSM models are very similar. However, precise
measurements at B-factories and hadron machines may be able to distinguish
these theories in terms of the other two CP-violating phases \alpha and \gamma.
This is illustrated for some representative values of the supersymmetric
contributions in \Delta M_d, \Delta M_s and |\epsilon|.
