  The shape of 3$d$-orbitals often governs the electronic and magnetic
properties of correlated transition metal oxides. In the superconducting
cuprates, the planar confinement of the $d_{x^2-y^2}$ orbital dictates the
two-dimensional nature of the unconventional superconductivity and a competing
charge order. Achieving orbital-specific control of the electronic structure to
allow coupling pathways across adjacent planes would enable direct assessment
of the role of dimensionality in the intertwined orders. Using Cu-$L_3$ and
Pr-$M_5$ resonant x-ray scattering and first-principles calculations, we report
a highly correlated three-dimensional charge order in Pr-substituted
YBa$_2$Cu$_3$O$_{7}$, where the Pr $f$-electrons create a direct orbital bridge
between CuO$_2$ planes. With this, we demonstrate that interplanar orbital
engineering can be used to surgically control electronic phases in correlated
oxides and other layered materials.
