Most "tanks" will have a passive that somewhat indicates it's a tank. But some character like Iruka and War Kiba might not be real tanks, they can soak alot of damage. You c*so just check stat distribution here.

http://image.prntscr.com/image/d90688a24fd742dba9afc1d6b672069a.png

You are looking for defensive stats Life, Resistance and Defense.
http://image.prntscr.com/image/453a6275daa840318434c0144a3deff2.png