Hi there,
As I don't own 12 string I can't get this exactly right but I believe it's one of
three things (or a combination):
(A) Capo on 3rd Fret
--2---2---2-------0-----------------------------|
----3-------3-------3---------------------------|
--------------------------0-2---0-2-------2-----|
------------------------0-----0-----0-------4-0-|
2-------2-----0-4-----0---------------0-4-------|
------------------------------------------------|
(B) Capo on 3rd Fret
[ Tab from: http://www.guitaretab.com/a/arcade-fire/251325.html ]
--2---2---2-------0-------6-8--6-8--------8-5---|
----3-------3-------3-------------------------6-|
------------------------------------------------|
------------------------0-----0-----0-----------|
2-------2-----0-4-----0---------------0-4-------|
------------------------------------------------|
(C) Capo on 3rd Fret (probably right)
--2---2---2-------0---------5-----5------8--5----|
----3-------3-------3-----8-----8-------------6--|
-------------------------------------------------|
------------------------0-----0-----0------------|
2-------2-----0-4-----0---------------0-4--------|
-------------------------------------------------|
I think the effect is slight vibrato (on a pedal) and that's it.
Cheers,
Raj