We demonstrate emergent antiferromagnetic interactions in strained thin films of the mixed valence manganite (Eu,Sr)MnO₃. Although the composition studied, Eu_0.7Sr_0.3MnO₃, will nominally yield a ferromagnetic phase in the bulk, we observe significant suppression of the saturation magnetization in films under both tensile and compressive strain. Despite the magnetization suppression, muon spin rotation spectrometry and polarized neutron reflectometry reveal uniform magnetic ordering in these films. Neutron diffraction and x-ray absorption spectroscopy demonstrate high-temperature G-type antiferromagnetic order in films under tensile strain, in contrast to the A- and C-type orders that are found in the phase diagrams of bulk (Eu,Sr)MnO₃ and other mixed-valence manganites. These probes also show that compressive strain results in a uniform but suppressed magnetization suggestive of moment canting resulting from competition between ferromagnetism and antiferromagnetism.