キヤノン 由来 one quickly finds the relevant official page for the origin of the name Canon.
It seems that the company name itself was derived from the English word "canon":
It was also a welcome coincidence that the pronunciation of キヤノン was close to 観音＝カンノン (Kannon, Kwannon, Avalokiteśvara):
In any case, the meaning of Canon was never meant to be directly related to カメラ.
As for the difference between キャメラ and カメラ we should first point out that カメラ is far more common. E.g. the Balanced Corpus of Contemporary Written Japanese (BCCWJ) gives
カメラ 5133 results
キャメラ 57 results
For the string
キャメラ there are a number of false positives from words such as キャメラマン, キャメラ・オブスキュラ. Looking at the results, it looks like キャメラ, if used at all, is more likely to be used in the context of filming.