The extreme spacetime environments of modified black holes are an ideal context in which
to study possible quantum corrections. This is critical for reconciling general relativity
and quantum mechanics and creating a theory of quantum gravity. In this dissertation,
I use canonical gravity methods to construct, reinterpret, and probe the properties of
quantum-corrected black holes, with the goal of refining modified gravity models, in the
pursuit of a theory of quantum gravity. First, I construct a quasi-classical static black
hole model with an additional scalar field introduced in the Hamiltonian constraint, and
I show that this quantum correction produces novel nonlocal quantum effects. Then, I
demonstrate that this model can be similarly constructed as a superposition of classical
black holes of varying mass by deriving a quantum modification to the Newtonian potential
in the asymptotic limit. Finally, I calculate the effect of a related quantum correction on
established volume calculations for the interior of the event horizon. Together, this work
provides key insights into the possible structures and behaviors of quantum black holes,
opening avenues to probe the information paradox, black hole "deaths," mass uncertainty,
and other mysteries of black hole physics. These advances lay the groundwork for
potential future predictions such as quantum switch behaviors around quantum black
holes, gravitational wave quasinormal mode observables from mergers of modified black
holes, and analog gravity connections to quantum gravity effects.