The process in which a relatively unspecialized cell acquires specialized features of a metanephric glomerular epithelial cell. Metanephric glomerular epithelial cells are specialized epithelial cells that form part of the metanephric glomerulus; there are two types, metanephric glomerular parietal epithelial cells and metanephric glomerular visceral epithelial cells. [ GOC:mtg_kidney_jan10 ]