Will this work in sonar?

Short answer: YES.
 
Depending on your setup, you can track audio from it into SONAR pretty simply.
 
The SR-18 has MIDI in, so you can send data from SONAR to it and trigger sounds. So YES.
 
You're gonna want a mixer or some other way to get audio from it into SONAR. It's more or less like any other external synth. You send it data from SONAR, it hears that and makes noise, and you track that back into SONAR.
 
I used an SR-16 waaaaaaaaaaay back in the day (and sheesh, so many albums from the 80's used that unit) with no troubles, so I expect no troubles with this unit.
 
The only thing i don't know off the top of my head (google will provide the answer I'm sure) is whether there's an .ins file for it already built.
 

I have both an SR-16 and SR-18.  But to be truthful the SR-16 is mostly used.  (I do primarily traditional country).
 
However, they both work with Sonar.  I run an analog output from the Left Main channel (for mono) to an input on my recording interface unit (A Roland Studio Capture). 
 
 

Thanks for the replies. I'm new at this so I'm just looking for suggestions any help would be appreciated. I really just want to be able to record guitar make some beats and put vocals on it. What's the best drum machine to get? Is their a device that allows you to plug your Guitar, mic, and drum machine in all at the same time and record what instrument you are using? Right now I have to record guitar, then plug in my mic to lay down vocals. I would imagine there is something that allows you to plug multiple things into your computer at once?

A "recording interface" (USB connected) with more than 1 input channel is what you want.  As you have three items, you would need a 4 channel device.   An example of a 4 channel device is the Roland Quad-Capture. 
 
An Alesis SR-16 would do the job and you can find them relatively cheap used.  Most of the other drum machines require programming.  There is the Addictive Drums that come with some versions of Sonar, but for basic beats the SR-16 will work OK.
 
 
 
 
 
 
 

Yah you don't need an external unit for that. SONAR has gobs of built in plugs that'll help you. Session Drummer, the Studio Instruments Drummer (is that included now?), and the biggie: Addictive Drums. You can just pick a kit, drag one of the MIDI grooves into SONAR's track pane, and BLAMMO, you've got your drums.
 

...wicked
Yah you don't need an external unit for that. SONAR has gobs of built in plugs that'll help you. Session Drummer, the Studio Instruments Drummer (is that included now?), and the biggie: Addictive Drums. You can just pick a kit, drag one of the MIDI grooves into SONAR's track pane, and BLAMMO, you've got your drums.
 

^ This.....
 
Unless you want the external unit for some other reason outside SONAR and I can't imagine what that would be other than for live performances.

If you're determined on using an external drum machine then for "traditional" drum sounds that take very little work to get sounding good and punchy in a mix the SR16 and 18 are good value. There's a reason they appear on so many recordings. Not so good for electronic drums though. One problem is that with the 16 it's difficult to build a kit with the same reverb (or no reverb) on everything.

The programming interface however is dreadful to use. I've used an SR-16 for years, but either sequenced from Sonar so it's just a sound module (used this way it has far more potential than when used standalone), or for live use created sequences in Sonar then played them into the SR-16's memory. Much easier than messing about with the less than reliable pads or the slow, menu-laden SR sequencer. For more electronic sounds or for a greater variety of sounds I use a Machinedrum, which is a much nicer thing to program and is much more capable.

For more natural (and cheaper, if you own Sonar but don't own an Alesis) Session Drummer and AD2 are both excellent. SD has less pre-processing already applied than the SR samples so takes a bit more work with eq and compression.

The Addictive Drums and EZ Drummer do not have anything that I can use.  I do (mainly) traditional country music.  Other than having a "real" drummer, the drum machines such as the SR-16 and 18 are the best thing for me. 
 
The "31A" in the SR-16 is my go to for country.  I did have to program in a 3/4 as there isn't one in the SR-16.  There are a couple of factory programmed 3/4's in the SR-18.