In answer to your question on canon, Disney == canon now. Only the movies and their directly related media in terms of novelizations, comics and video games are now canon. Also included are Clone Wars and Rebels animated series and their related material. All previous EU material is now considered "Legend" and not strictly canon.
In regards to the cross-guard, if you mean specifically this design as opposed to cross-guards in general (which Richard covered):
This cross-guard is old and unique
From the wiki article:
The lightsaber was crudely assembled based on an ancient design dating back thousands of years to the Great Scourge of Malachor, and thus featured seldom-seen crossguard blades. A single cracked Kyber crystal, barely able to contain the weapon's power, necessitated the lateral vents which produced these crossguard quillons and gave the weapon's red plasma blades an unstable, serrated appearance.
So in terms of canon, this lightsaber has never been seen as it pre-dates the events of TPM by a millennia or so. Second, it's unique to even that design because of the jagged appearance of the blade itself which is specifically due to Kylo's crystal.