Cosmic rays (CRs) propagate in the Milky Way and interact with the interstellar medium and magnetic fields. These interactions produce emissions that span the electromagnetic spectrum, and are an invaluable tool for understanding the intensities and spectra of CRs in distant regions, far beyond those probed by direct CR measurements.
We present updates on the study of CR properties by combining multi-frequency observations of the interstellar emission and latest CR direct measurements with propagation models. Finally, we make prediction for e-ASTROGAM and AMEGO, proposed gamma-ray missions with special focus at the MeV energy range.