Surface-enhanced Raman scattering (SERS) is a highly advantageous analytical technique for detecting trace biological and chemical compounds. However, significant challenges remain in the cost-effective fabrication of large-area and homogenous SERS substrates. A simple and scalable approach utilizing a layer-by-layer spray deposition followed by thermal annealing is proposed to fabricate cellulose nanofibril (CNF) films loaded with gold nanoparticles (Au NPs) and graphene oxide (GO) hybrids as SERS substrates. These hybrid 3D structures comprising CNF/Au NPs/GO significantly enhance SERS sensitivity by both electromagnetic enhancement and chemical enhancement. Incorporating CNF as a 3D network enables a more uniform distribution of Au NPs/GO. Thermal annealing further induces hotspots. For instance, the annealed CNF/Au NPs/GO hybrid thin films achieve a detection limit of 1.0 x 10^-13 m and a high enhancement factor of 4.97 x 10¹¹ for Rhodamine 6G. Grazing incidence small-angle X-ray scattering combined with nano-Fourier-transform infrared spectroscopy is first used to confirm the combined Raman enhancement mechanism of localized surface plasmon resonance and interface charge transfer with high spatial resolution. Therefore, the proposed methodology establishes a robust framework for the scalable fabrication of ultrasensitive SERS substrates.