A close study of two early texts in Buddhism and Brahmanism show that Buddha and Vishnu are two separate beings.
In the Maha-samya Sutta there was an occasion when the devas from almost all the planes came to see the Buddha when he was dwelling in the Great Wood together with 500 bhikkhus, all of them arahants. The Buddha introduced their names to the monks, Vishnu was one of those present. The Buddha mentioned him by the name Venhu.
The Venhu Sutta shows Vishnu as one of the young devas who came to visit and talked with the Buddha:
At Savatthi. Standing to one side, the young deva Venhu recited this verse in the presence of the Blessed One: " Happy indeed are those human beings attending on the Fortunate One. Applying themselves to Gotama's Teaching, who train in it with diligence." The Blessed One said: "When the course of teaching is proclaimed by me, O Venhu," said the Blessed One, "Those meditators who train therein. Being diligent at the proper time. Will not come under Death's control."
According to "Hinduism and Buddhism An Historical Sketch", Sir Charles Elliot who was a British diplomat mentioned that this correlates with the Rig Veda text before Hinduism started. Both texts mentioned that Vishnu and Shiva are minor deities instead of the Lords of the Universe as popularly known by worshippers:
" Vishnu and Rudra (Shiva) are known even to the Rig Veda but as deities of no special eminence. It is only after the Vedic age that they became , each for his own worshippers, undisputed Lords of the Universe…..The Pali Pitakas frequently introduce popular deities , but give no prominence to Vishnu and Siva. They are apparently mentioned under the names of Venhu and Isana, but are not differentiated from a host of spirits now forgotten. ….The suttas of the Digha Nikaya in which these lists of deities occur were perhaps composed before 300 B.C. "- Sir Charles Elliot
The texts above included quotes from the Pali canon showing that Buddha and Vishnu are two different people. It is supported by the Charles Elliot's comparative studies of early Hindu and Buddhist texts before the changes that take place in later texts. His book is called " Hinduism and Buddhism a Historical Sketch. There are three volumes that goes into detail on the subject. The quote above is from Vol. 2 page 746. The other is from The Connected Discourse of the Buddha" A Translation of the Samyutta Nikaya by Bhikkhu Bodhi ,page 432).
