Like I said, the "canon" we use in the English discourse actually has at least two separate meanings.
One is the authoritative body of work. For our purpose, the adjective 公式
koushiki (official) is enough. The
Sherlock Holmes fandom knows about 正典
seiten (canon) and 外典
kaiten (apocrypha), but for everybody else they are just biblical terms.
The other is the currently maintained continuity. The word for that should be 正史
seishi (officially composed history, sanctified history), as opposed to 非正史
hi-seishi (non-sanctified history). That's the word you use when you want to determine whether a piece of officially published fiction still "counts" for the universe, which is what Touhou fans mean when they debate whether the PC-98 games are canon. E.g. see the Japanese wiki for Star Wars and Star Trek.
Of course there's also fanon. Fanon, or fan-made ideas in general, are called 二次設定
niji settei (secondary
settei), just as fan works are 二次創作
niji sousaku (secondary creation, generally translated as "derivative works"), hence canon as its opposite is 一次設定
ichiji settei (primary
settei). For obvious reasons, you probably don't want to use the latter before ZUN.
設定
settei, literally "establishment; configuration", is a word originating from Edo era theatre, and for fiction refers to everything that forms the backstory: stage setting, worldbuilding, art design, characterization, history of events, and so on.
TL;DR:
Official continuity:
正史
seishi "sanctified history", thankfully a real life word normal people knows.
The opposite of fanon:
一次設定
ichiji settei "primary worldbuilding / characterization / etc.", fan speak, normal people won't understand.
Authoritative body of works:
Just call it 公式作品
koushiki sakuhin "official works" or official whatever. Don't bother with 正典
seiten, カノン
kanon, キャノン
kyanon or other translations of canon.