Regardless of what it is, the only reasonable response is to defend.
In starcraft you can invest your resources into: Army, Economy and Technology.
Think of it in terms of sacrificing one for another or investing in one and sacrificing the other two.
So the reason you should defend is that you have invested more money on your economy with your expansion at the expense of your technology and army. whereas he has sacrificed his technology for more army (2nd rax instead of fact) as well as having a weaker economy than you.
So to sum up your tech is probably about even, your economy is much stronger than his and his army is much stronger than yours (or at least will be soon since he has double the production buildings).
This means that you have to defend since you're weaker in the near future. In the long run (if he doesn't manage to damage your economy with his superior army) you will far exceed him in both army and technology. So essentially if you simply defend you will be quite far ahead and can then roflstomp your opponent later on.
So to defend you'll probably want at the very least one bunker, two or more is more than fine. Consider walling off your natural (if it's small enough), another thing you can do is wall off the bottom of the ramp, a depot and a bunker is enough for this, and then have another bunker near your expansion so they can't get into your main and your natural is defended too.
You may want to cut scvs or not, depending on how safe you feel, you could put down a few more barracks with the extra money, you have an expansion already so you're undoubtedly ahead in economy so it's not the worst thing to sacrifice some workers (some economy) for a bit of a stronger army to defend better.
I doubt that cutting probes is necessary if you position your bunkers properly, and repair them.
As to what they are doing it's hard to tell, they are probably doing some quick push with the rax units, unlikely stim, it could be marauders or reapers, or simply a reactor for more marines. So if there's a chance that its reapers then make sure you put some marines (or even a bunker if you're scared) to defend your workers in your main.
What you can do is scout again, (try and keep your original scout alive and nearby) a little later on, just send it up the ramp and see what he has, whether it be marines or marauders or reapers. If you don't see (m)any units it's likely that it's reapers and they're on the way already. Just try and get more information. If you're unsure then send another scv to outside his base so that when he moves out with his army you will see what he has, this will give you a small amount of time to build up even more defense now that you know exactly what's coming.
Another big possibility (especially if you didn't see tech labs/reactors building with your scouts) is that there's a proxy factory, possibly widow mines or hellions. Sometimes people will float it into your base and make mines, which can be quite devastating. Again, bunkers in your main and nat will stop both of these.
As long as you don't sacrifice too much economy for an attack that isn't actually coming (maybe he goes two rax into triple expansion? haha) it will turn out well for you. It's unlikely though since he has even sacrificed his orbital, for a stronger army, so if he doesn't attack he'll be so far behind on economy that you can just win with any half assed attack.
So just keep trying to get as much information as you can, while preparing for everything that it COULD be, with more information that you get you can tailor your defense to exactly what is coming.