So if this is straight from the website, doesn't it make it canon?
It's a tad trickier than that since the Japanese materials are what the fandom tends to regard as actual canon, smoothing over or exposing continuity issues that may be created at times even in official localizations (e.g. Noel being "the last child to be born [only not really]" in XIII-2).
FFXV's bizarre English localization vs. Japanese vs. other localizations has taken us into uncharted territory in this regard (the Japanese version actually has less canon info at times than the unsurpassed German localization), but this rule of sorts about the Japanese material taking precedent as canon is generally the standard to follow. This leaves the status of "Gaia" as the FFVII planet's name in a place somewhat comparable to the old "Star Wars" continuity, where stuff like "The New Jedi Order" was official yet not necessarily canon (to George Lucas).
In the past, I've personally scoured every available piece of Japanese material on FFVII that I could and never found anything identifying the planet as anything but that generic word.
... That being said, "Gaia's Cliffs" is indeed the name of that area, so it may well be that this was intended to be the name of the planet at some point in the game's development, and it just never got any explicit reference in Japanese material (for whatever reason). I'll honestly be kind of surprised if they don't just go ahead with this as the planet's name in the remake, as a more fleshed-out presentation of this game's world will kind of demand an explanation for the name given to this no man's land at the end of the world.