Surya is sitting in Padmasana. The back of the bronze is not worked on and this is typical of the region where this bronze is from.
The peaked tiara with central crown and double lotus pedestal are typical of bronzes from Bihar/Bengal.
This bronze appears to be single cast. It is about 5.7 cm in height. This is from Pala period (10-11th century).
There is one more example of seated Surya on this site. That page has more information on Surya and other examples. The image is reproduced below for comparison.