The West German G3 is a 'battle rifle' and was the 'right hand' of NATO countries. It was bulky and large to have, but reliable, accurate, and powerful. Even to this very day, the G3 is still used by many armies and even the Iranian forces (the horror) has adapted the rifle. The G3 was the first 'true' modern rifle and the design was copied by many forces.
The G36 series is a modern assault rifle which currently fit the need of the German forces. It is the first true assault rifle to be adopted by both West and East Germans and causes some problems as the East Germans was using Soviet made weapons and their own designs. The G36 series is lighter, more modern, sleek, and easy to take care of and use. However, the gun lacks stopping power unlike the G3, which is odd in Combat Arms as the G3 should have more firepower.
The G36E is a specific form of the G36 series, it only have the single scope, while the normal G36 series have two, an optic scope and a simple 'iron scope' for use at close range. The G36E is only give to Spain and Latvia and no other countries, which is odd to see that in CA.