I didn't know this was an issue XD
But god this news is so huge, I wanna know how it went unnoticed for so long. Haven't people been studying the Ultimanias for years? ... I still don't get how we just noticed this now XD And I think anyone can tell the high affection version is canon...
I think Ryu is right. It's just that there are so many instances of "communicated their feelings to each other" (one in the CC Ultimania, two in the Ultimania Omega) or "disclosed their feelings to each other" (one in the Ultimania Omega, one in the 10th Anniversary Ultimania), that this one -- which actually appears in the paragraph below an instance of "communicated their feelings to each other" on pg. 27 of the UO -- just got overlooked.
So, yeah, there's six quotes like this in total, and this one was just easy to miss. I blame myself, really. I started to translate the whole page once and didn't do it.
In any case, this version of the scene is definitely canon, I believe. Not only is it the only version that really fits all those descriptions, and not only is it also the only one talked about in the FF 20th Anniversary Ultimania Scenario book's summary of the story, but I just asked FF_Goddess to check her FFVII Memorial Album (published by DigiCube/Square way back in 1999) to see which version of the scene it included in its script of the whole game.
She said it only mentions the high affection version, and that it's across pp. 241 through 242 in a section called "Highwind."
So, yeah. I think for those who Cloud and Tifa sexing it up that night is the grand indication of Cloud's romantic desire, this will resolve things. I'm sure there will still be some folks who feel it isn't enough, but that's what the Compilation is for.