From the experts:
This appealing name has a good chance of catching on due to the popularity of Ewan McGregor, and the trend towards Gaelic names in general. Pronunciation is YOO-un.
Ewan has a complex family tree, with connections to John, Owen, Hugh, Evan and Eugene. Other spellings are Ewen, Eoin and Euan.
In Willa Cather's novel My Mortal Enemy, there is a character called Ewan Gray.