We investigate intermodal forward Brillouin scattering in a solid-core PCF, demonstrating efficient power conversion between the HE11 and HE21 modes, with a maximum gain coefficient of 21.4/W/km. By exploring mechanical modes of different symmetries, we observe both polarization-dependent and polarization-independent intermodal Brillouin interaction. Finally, we discuss the role of squeeze film air damping and leakage mechanisms, ultimately critical to the engineering of PCF structures with enhanced interaction between high order optical modes through flexural mechanical modes.