The Zeiss
ZE lens is Canon mount (it's also offered in other mounts, such as ZF for Nikon).
This really is apples vs oranges, trying to compare these two lenses. Yes, both are 50mm lenses, and both are ultra high quality.... but that's about where the similarities end. They serve very different purposes and are designed to render images differently.
The Zeiss 50mm f2 Makro-Planar is all about being able to deliver uncompromising sharpness from edge-to-edge with durable, high precision, all-metal build quality. It is a macro lens optimized for very close focusing. And, like all the Zeiss lenses for other camera systems, is strictly manual focus and can focus as close as 9.5 inches, for 0.5X or 1:2 or half life-size magnification.
The Canon 50/1.2L is almost the opposite... It's all about beautiful background blurs and soft transitions and is typical very high quality and durable L-series build and environmental sealing. It's optimized for portrait shooting distances and is a popular wedding lens for the dreamy image qualities it can render. It has autofocus, though it's not the fastest USM lens Canon offers. It's not optimized for close up, by any means, but can focus to about 18 inches, giving 0.15X or a little less than 1/6 life-size magnification.
Both lenses are usable for other purposes, of course, but are somewhat specialized. They aren't really your typical "normal" walk-around lenses (though they can be used that way, if you wish). Canon EF 50/1.4 USM, EF 50/1.8 STM and Zeiss 50/1.4 ZE are more "normal" lenses.
The Canon lens is a little bigger (72mm filters vs 67mm) and slightly heavier.
You can compare the two lenses side-by-side on
www.the-digital-picture.com. Both are thoroughly reviewed and tested there.
The Zeiss b ZE /b lens is Canon mount (it's also... (