To use a CO2 fire extinguisher for general obscurement, I'd suggest having it be in a Cone Template and having the the area sprayed grant "Light Cover", because that's described as "half or less of the target is obscured, which sounds about right for a light, gaseous propellant that moves quickly.
Against humans, I think the easiest thing to do would be to use the blind power and have its trapping be a CO2 fire extinguisher. This gives targets a chance to make an Agility roll at –2 (–4 with a raise). Failure means that they are Shaken and have –2 Parry. If they roll a 1 on the Agility die, they are also at –6 to Trait rolls requiring vision for as long as they are Shaken.
I'd say make the CO2 fire extinguisher a limited use object that can "cast" the blind power on a Cone Template. These things are pretty easy to use, so I'm inclined to make there be no skill roll needed (although you could add one to reflect how accurately you can point it).
Against inanimate surfaces, I'd just include in the description that it lowers the temperature of the surface. There's not really a good mechanical way to model this given the wide variety of materials, so I'd just leave it to the GM to adjudicate what that means.
One thing you could do is add the Cold Trapping. The Fatigue one (Vigor roll or take one level of cold-based Fatigue) makes sense given that using this on a person is dangerous as it could result in frostbite, but the trapping says that range should be halved (not possible with a Cone Template) or power point cost should be doubled. The latter could be achieved by having a low number of uses.
Speaking of how many uses, I'd suggest taking a page Savage Worlds Showdown and just make it a random die roll to see whether they ran out or if there is at least one more shot. Given the Cold Trapping, I'd say roll a d6 after each use and on a 6, it's out (which given that these things last 20 seconds or so, seems about right).
Putting it all together:
CO2 fire extinguisher
A C02 fire extinguisher is designed to quickly extinguish a fire by lowering the temperature and displacing oxygen. It can be sprayed in a Cone Template as an action. Unlike other fire extinguishers, C02 does not leave any residue behind.
In a pinch, it can be used as a weapon. As an action, the wielder can spray the C02 on targets in a Cone Template, effectively using the blind power with the Cold: Fatigue Trapping against them. No roll is needed to activate the CO2 fire extinguisher and so all "arcane skill" rolls are considered successful (with no chance for a Raise). After every use, roll a d6. On a 6, the fire extinguisher has run out of C02 and can no longer be used.
The area sprayed by the extinguisher provides Light Cover (-1 to attack rolls) for all attacks that target an individual inside the Cone Template or on the opposite side of the Cone Template until the wielder's next turn.
The canister can also be used as an improvised weapon. It counts as one size larger when full.