As a former Terminator fan, I recall in our old fan-base we always had to deal with the similar dubious canon of a Universal Studios attraction called T2-3D: Battle Across Time, in which James Cameron was also involved. The plot of the attraction broke the existing Terminator lore as well, but because time travel is central to the plot of the Terminator franchise, it could more or less be put into an alternate timeline. But still it broke some internal logic of the franchise and subsequent movies never made any reference to it. Generally we took only the interesting things as canon and discarded what didn't make sense, since there were no clear canon guidelines anyway.
In case of the Avatar attraction from Disney, I would say I didn't like the concept when I first heard of it. Firstly, I thought the whole plot and setting felt too sugary and as subtle as getting an anvil with morals carved into it dropped onto your head. Secondly, I think the Avatar franchise just doesn't work well as a physical park attraction. It just goes against the central logic of the franchise, by being dumbed down and turned into capitalistic merchandise. Also, since Na'vi culture draws so heavily from existing human cultures, putting those on display in a physical park like that just feels wrong to me.
Apparently, according to Joshua Izzo, this attraction, officially called Pandora: The World of Avatar is indeed canon.
