One thing to keep in mind, the 70D has been produced in two different versions. A version with and one without WiFi. Ensure you are certain that one of the two cameras you have is not the WiFi-less type of the 70D. This can be seen on the label on the bottom of your camera, it should state if it is a 70D (W) or a 70D (N) where the ‘N’ version is the WiFi-less variant.
Otherwise it might be as Aganju suggested in his answer, that an already enabled setting prevents you from enabling WiFi at this moment.