  We define the notion of a $\Lambda$-system of $C^*$-correspondences
associated to a higher-rank graph $\Lambda$. Roughly speaking, such a system
assigns to each vertex of $\Lambda$ a $C^*$-algebra, and to each path in
$\Lambda$ a $C^*$-correspondence in a way which carries compositions of paths
to balanced tensor products of $C^*$-correspondences. Under some simplifying
assumptions, we use Fowler's technology of Cuntz-Pimsner algebras for product
systems of $C^*$-correspondences to associate a $C^*$-algebra to each
$\Lambda$-system. We then construct a Fell bundle over the path groupoid
$\Gg_\Lambda$ and show that the $C^*$-algebra of the $\Lambda$-system coincides
with the reduced cross-sectional algebra of the Fell bundle. We conclude by
discussing several examples of our construction arising in the literature.
