Shoot color charts on both under the same lighting conditions, and see how they look.
All of this can be done with a calibrated monitor, scopes, experience, and time. Be warned that sometimes you have to take the better camera and degrade it to look like the cheaper camera. It's rarely possible in my experience to take a cheap camera and improve it to make it look like a more expensive camera. I have done shows that had Red, mid-level Sony, and Canon 5Ds shooting the same scene, and much of the time the best I could do was whack the Red and Sony footage and make it look as bad as the 5D. It all matched and the director was happy with the results.