There is a possible case in Ireland, though it is not certain: Saint Brigid. This from Wikipedia:
There is some debate over whether St Brigid was a real person. She has the same name, associations and feast day as the Celtic goddess Brigid, and there are many supernatural events, legends and folk customs associated with her.
Some scholars suggest that the saint is a Christianization of the goddess, others that she was a real person whose mythos took on the goddess’s attributes. Medieval art historian Pamela Berger argues that Christian monks “took the ancient figure of the mother goddess and grafted her name and functions onto her Christian counterpart”. Professor Dáithí Ó hÓgáin and others suggest that the saint had been chief druid at the temple of the goddess Brigid, and was responsible for converting it into a Christian monastery. After her death, the name and characteristics of the goddess became attached to the saint.
– Wikipedia Brigid of Kildare
As has already been noted, the Buddha was made a Christian saint: Saint Josaphat.