  Two-body charmless nonleptonic decays of $B_u \to V V$ are studied within the
generalized factorization approach using a recent calculation of the effective
Wilson coefficients $c^{eff}_i$, which are not only renormalization-scale and
-scheme independent but also gauge invariant and infrared finite. After making
a universal ansatz for the nonfactorizable contributions, we parametrize these
effects in terms of $N_c^{eff}(LL)$ and $N_c^{eff}(LR)$, the effective numbers
of colors arising from $(V-A)(V-A)$ and $(V-A)(V+A)$ four-quark operators,
respectively. Three different schemes for these contributions are considered:
(i) the naive factorization, (ii) the large-N_c improved factorization, and
(iii) our preferred choice: $(N_c^{eff}(LL), N_c^{eff}(RR))=(2,5)$. We present
the full angular distribution of all charmless $B_u \to V V$ decays in both
transversity and helicity frames.Direct CP violation in these normalized
angular correlation coefficients is not negligible in $B^-_u \to K^{*-} \rho^0,
K^{*-} \omega$, and direct CP violation in the partial rate difference for
$B^-_u \to K^{*-} \omega, K^{*-} \rho$ and $\rho^- \omega$ can be as large as
45%, 25%, -10%, respectively. Due to the sizable QCD penguin contributions in
$\rho^- \omega$, the determination of the unitary triangle $\alpha$ via this
decay mode is more promising than via $\rho^- \rho^0$. It is also encouraging
to determine the unitary triangle $\gamma$ through $B^-_u \to K^{*-} \rho$
because of $N_c$-insensitivity and the not-so-small tree contribution. The
impacts of a negative $\rho$ on the branching ratios and CP violation are
studied. We also comment on the theoretical uncertainties and their possible
impacts.
