Cerium-doped LaMnO₃ is widely discussed as one of the most prospective electron-doped thin-film prototype material that complements well-established hole-doped mixed-valence manganites. Here, we investigate La_0.7Ce_0.3MnO₃ films with respect to their electrical properties and check whether they provide an effective electron doping with Mn-valences well below +3. Thin films of a variable thickness between 10 and 100 nm are characterized through resistance measurements over a broad temperature range between 90 and 300 K deducing their hopping energies, carrier localization lengths, and the Mn valence by comparing the experimental data to different transport models. While electronic transport above 300 K is well determined by the thermally activated diffusion of small polarons, we find the carrier localization by disorder to reveal a variable-range hopping-type transport for lower temperatures. From the several parameters investigated in the study, it is mainly the oxygen content and the degree of CeO₂ phase segregation that are crucial to be controlled in such electron-doped thin-film manganites.