Feel free to update this. I pulled this from another source so it's possible that some of this may be inaccurate or outdated.
This is what is supposedly confirmed as far as MW3's weapons are concerned.
Sniping Rifles:
PSG-1
RSASS
Barret .50 cal
M14 EBR
SMGS:
Scorpion
MP5
AK-74u
P90
UMP45
Assualt Rifles
SCAR-L
G36C
ACR
AK-47
M4
FAMAS
Shotguns:
Model 1887
Striker
KSG
AA-12
Spas-12
Pistols:
MP412
Walter P99
Magpul FMG
G18
Launchers
RPG
XM25 (IAWS)
Add pictures, comments, and any updates that you see!