Starch-based films have potential on food packaging applications due to their minimal environmental impact. This study aims to enhance tensile strength and moisture barrier properties of cassava starch/chitosan/gallic acid films by incorporating different amounts of canola straw cellulose nanofibers (CNFs). Films were produced in subcritical water media and the effect of temperature and CNFs content were investigated. Films were characterized for structural, mechanical, physico-chemical, optical and functional properties. The use of 0.1 g CNFs/g starch showed 12.7 times improved tensile strength compared to the film without CNFs. Because of the hydrophobic CNFs, films improved moisture resistance with a reduction of water vapor permeability and film solubility in water. Moreover, ester linkages and hydrogen bonds between starch, chitosan, cellulose, and gallic acid were confirmed by FT-IR spectra, reducing free gallic acid release from the film. CNFs are promising fillers to starch-based films to improve tensile strength and moisture barrier properties.