The polarization properties of long-period gratings inscribed in highly birefringent photonic crystal fibers are investigated in the context of a multipole method analysis. It is demonstrated that by proper design such fibers may act as selective polarization elements, showing an ample separation of the resonance peaks corresponding to the two orthogonal polarization states. Furthermore, the infiltration of the fiber's capillaries with an isotropic liquid may lead to extensive tuning of the resonant wavelengths. A tuning efficiency of up to 10 nm/°C is demonstrated in the case of a typical infiltrated birefringent photonic crystal fiber.