  The lensing convergence measurable with future CMB surveys like CMB-S4 will
be highly correlated with the clustering observed by deep photometric large
scale structure (LSS) surveys such as the LSST, with cross-correlation
coefficient as high as 95\%. This will enable use of sample variance
cancellation techniques to determine cosmological parameters, and use of
cross-correlation measurements to break parameter degeneracies. Assuming large
sky overlap between CMB-S4 and LSST, we show that a joint analysis of CMB-S4
lensing and LSST clustering can yield very tight constraints on the matter
amplitude $\sigma_8(z)$, halo bias, and $f_\mathrm{NL}$, competitive with the
best stage IV experiment predictions, but using complementary methods, which
may carry different and possibly lower systematics. Having no sky overlap
between experiments degrades the precision of $\sigma_8(z)$ by a factor of 20,
and that of $f_\mathrm{NL}$ by a factor of 1.5 to 2. Without CMB lensing, the
precision always degrades by an order of magnitude or more, showing that a
joint analysis is critical. Our results also suggest that CMB lensing in
combination with LSS photometric surveys is a competitive probe of the
evolution of structure in the redshift range $z\simeq 1-7$, probing a regime
that is not well tested observationally. We explore predictions against other
surveys and experiment configurations, finding that wide patches with maximal
sky overlap between CMB and LSS surveys are most powerful for $\sigma_8(z)$ and
$f_\mathrm{NL}$.
