There is no single Buddhist canon. There are several, in different languages, preserved by traditions that separated early, and the differences between them are the main evidence for how the pantheon developed.
The Pali Canon of the Theravada is the most complete early collection surviving in an Indic language, committed to writing in Sri Lanka after centuries of oral transmission by reciters trained in specific portions. Its formulaic, repetitive style is a feature of that transmission rather than a stylistic failing.
The Chinese canon preserves translations of texts whose Indian originals are lost, including versions of the early collections belonging to schools other than the Theravada, so a comparison between the Pali and the Chinese can show what one school added or dropped. The Tibetan canon does the same for the later Indian material, and preserves the tantric literature most fully.
The Mahayana sutras present the sharpest question of all. They appear centuries after the Buddha, describe vast assemblies of buddhas and bodhisattvas, and claim the authority of his word. How that claim was understood and defended within the tradition is itself a substantial subject.
Alongside the texts, inscriptions, monastic architecture and image-making supply a record of what was actually venerated and when, which does not always match what the texts prescribe. The earliest Buddhist art avoids depicting the Buddha's body at all.