Investigations of polarons in a polar cylindrical quantum wire are carried out for various barrier potentials at the interface. It is shown that dependencies of the ground-state energy and the effective mass on the radius of the wire may be used in order to determine the mechanical boundary conditions in a heterostructure under consideration. In the presence of a magnetic field directed along the wire axis, the Schrödinger equation with a centred parabolic potential within the wire is solved exactly and the energy spectrum depending on the magnetic field is obtained. As far as a splitting and a pinning of the energy levels of magnetopolarons are revealed to depend on the electron-phonon interaction, they can be used for an effective characterization of the state of interfaces in nanostructures. A relative intensity of absorption for the different polarizations of light determines the degree of non-perfectness of the interfaces. The geometrical features of interface can be characterized by means of the cyclotron and the cyclotron-phonon resonances.