The lens had a CPL, not the Rebel ...

The 24-70 f/2.8L II provides rich colors alone, particularly the series II version. You might try it for a month or so and see if you feel you need a CPL for this lens. Otherwise, you get what you pay for, and if you find you need a CPL, the B+W XS-Pro Kaesemann line is one you buy once and use forever (or at least as long as you have a need for an 82mm filter thread). Look to see if you can find a used one, such as KEH or Adorama, eBay, etc.

If you feel you're not getting better results vs your prior camera, you should post some JPEG unedited examples storing the file attachments, and let's get some other eyes onto the results and see what is going on.