you can see, the P20 will have the fingerprint button on its front, while the P20 Plus moves it to the back in order to cut the bottom screen bezel ever so slightly more. This design of the P20 was confirmed by what we've seen from TENAA yesterday.
The P20 Plus seems to be the only phone in the line to actually sport the much-leaked tri-lens rear camera, unless we're also getting a (sometimes rumored) P20 Pro. To add to the confusion, it's entirely possible that the Plus and Pro are one and the same device.
A different leak talks about the specs of the model it calls P20 Pro, which should come with a 6" 2,160x1,080 touchscreen, the Kirin 970 SoC at the helm, 6/8GB of RAM, 128/256GB of storage, and a 4,000 mAh battery.