We investigate an ensemble of systems formed by a ring enclosing a magnetic flux. The ring is coupled to a side stub via a tunnelling junction and via Coulomb interaction. We generalize the notion of level hybridization due to the hopping, which is naturally defined only for one-particle problems, to the many-particle case, and we discuss the competition between the level hybridization and the Coulomb interaction. It is shown that strong enough Coulomb interactions can isolate the ring from the stub, thereby increasing the persistent current. Our model describes a strictly canonical system (the number of carriers is the same for all ensemble members). Nevertheless for small Coulomb interactions and a long side stub the model exhibits a persistent current typically associated with a grand canonical ensemble of rings and only if the Coulomb interactions are sufficiently strong does the model exhibit a persistent current which one expects from a canonical ensemble.