Far-infrared line emission provides key information about the gas cooling and heating due to shocks and UV radiation associated with the early stages of sta r formation. Gas cooling via far-infrared lines might depend, however, on metallicity. We aim to quantify the far-infrared line emission, determine the spatial distribution of CO rotational temperature, ultraviolet (UV) radiation field, and H2 number density toward the embedded cluster Gy 3-7 in the CMa-l224 star-forming region, whose metallicity is expected to be intermediate between the Large Magellanic Cloud and the Solar neighborhood. By comparing the total luminosities of CO and [OI] toward Gy 3-7 with values found for low- and high-mass protostars extending over a broad range of metallicities, we also aim to identify the possible effects of metallicity on the far-infrared line cooling within our Galaxy. We study SOFIA/FIFI-LS spectra of Gy 3-7 covering several CO transitions from J=14-13 to 31-30, the OH doublet at 79um, the [OI] 63.2 and 145.5um, and the [CII] 158um lines. The field-of-view covers a 2'x1' region with a resolution of ~7"-18". The spatial extent of CO high-J (Jup>=14) emission resembles that of the elongated 160 um continuum emission detected with Herschel, but its peaks are offset from the positions of the dense cores. The [OI] lines at 63.2um and 145.5um follow a similar pattern, but their peaks are found closer to the positions of the cores. CO transitions from J=14-13 to J=16-15 are detected throughout the cluster and show a median rotational temperature of 170+/-30K on Boltzmann diagrams. Comparison to other protostars observed with Herschel shows a good agreement with intermediate-mass sources in the inner Galaxy. Assuming an origin of the [OI] and high-J CO emission in UV-irradiated C-shocks, we obtain pre-shock H_2_ number densities of 10^4^-10^5^cm^-3^ and UV radiation field strengths of 0.1-10 Habing fields (G0). Far-IR line observations reveal on-going star formation in Gy 3-7, dominated by intermediate-mass Class 0/I young stellar objects. The ratio of molecular-to-atomic far-IR line emission shows a decreasing trend with bolometric luminosities of the protostars. However, it does not indicate that the low-metallicity has an impact on the line cooling in Gy 3-7.