We show that both the flux and the cutoff energy of protons accelerated by ultraintense lasers can be simultaneously increased when using targets consisting of thin layers of bundled nanochannels. Particle-in-cell simulations suggest that the propagation of an electromagnetic field in the subwavelength channels occurs via excitation of surface plasmon polaritons that travel in the channels down to the end of the target, sustaining continuous and efficient electron acceleration and boosting acceleration of protons via enhancement of the target normal sheath acceleration mechanism.