Firmware 3.0 supports tethering, certainly.
I have two Canon 5D3's, the original 7D and two Fuji cameras - the X100S and the X-T1. The one place the Fujis fall down is focus speed, compared to the 5D3. I plan to keep the Canons simply because I like to shoot birds in flight, and the x-T1 is not particularly good at that. Well, I might unload one 5D3 to get fundage for more X glass..
On the other hand, the X-T1 went to Mexico with me in November and I had a blast with it there. Managed to grab some images that I am very proud of. Based on my experiences there, I can say the X-T1 would be my first choice for landscape and portrait photography, while the 5D3 will remain my go to camera for birds and other active shooting. Here are a few samples.
The sunset was taken with the 18-55 kit lens from a tripod, several shots stitched in Photoshop. These were the jpgs straight out of the camera.
The cormorant was the 55-200 handheld at 200mm 1/60 second.
The cat was the 35mm f1.4 shot wide open with available light, indoors, hand held at 1/60 second.