Sonar producer 8.5.3 user here. As I only get down to composing and recording a song about once a year, I sadly often forget how to do things like this.

Route the mono tracks to a bus, panning the tracks hard L and R. Then you can either use the bus as a stereo track or bounce the bus to create a stereo track.

In a way there's no reason to even do this, just pan them where you want. Done.
 
Mono tracks are a much better idea as you have more options when mixing later. Stereo tracks are rarely used in a multi track recording. Pre recorded sound sources and loops ya. Then some hardware synths or a stereo guitar processor you could use a stereo track but I would still use 2 mono tracks for those as well. Then pan hard L-R
 
But to answer your question, Pan the tracks, then choose "bounce to track" and to "stereo" track and it will create a new stereo track of the 2 monos.  

Scook... HA... I've resorted to that before, but swore there was a shortcut somewhere allowing me to directly bounce two tracks to a new one. I've tried this and ended up with the two sources being mixed, so that's not what I want. But I still think maybe I'm missing a shortcut to doing it on one step.

If the result is mixed, you did not pan the tracks before bouncing.

Scook... Yes, you're ight... the first time I tried this I neglected to PAN the trcks, BUT...
 
Cactus, Even when I DO pan the two tracks, its not the expected result. What happens is this. I select my two tracks, panned hard left and right, then select bounce the Tracks, select Steroe, and select "Tracks" as my source. This makes the two tracks I want to bounce show up in the source window. And, the "Destination" shows just one "New" track. But after I do the bounce, what I get is TWO new tracks. Both of them are stereo, but one contains one source track on the "L" side with the "R" side empty, and the other contains the second track on the "R" side with the "L" side empty. I guess I could try bouncing those two tracks again, but based on the behavior above I'm pretty sure I'll end up with another two tracks.

I see your point about just keeping the two tracks Mono, and indeed this is case of two very similar guitar tracks for fullness. The reason i wanted one stereo is because I now see that it would be very helpful to control them both with a single volume envelope, mainly to back them off some during vocals and such. I could just route them to a new bus with a new track envelope, and then route that bus output to the master or back to my original "instrument" bus. I just hate to further clutter my bus area for such a simple operation, and I still wouldn't mind learning to bounce to a single stereo track and get the desired effect (One stereo track).

That is why you need a bus to use as the source. So both tracks are combined into a singe track before the bounce. I guess you could use master out, I never have.

I do not use any bus. I pan them L and R and export audio. I would not need them in one track till the final product. There some "Convert to Stereo" and Convert to Mono" options- I never had to use them- it is above the tracks view.
 
Also-I find it ignorant, posting that nobody uses stereo tracks.

peterpan
 I just hate to further clutter my bus area for such a simple operation.

Not to dissuade you from your quest, but you may find that the benefits of this approach outweigh the minimal clutter.
If you bounce the source tracks to new tracks, you now have more tracks in the project to manage. Sure, you can delete or archive the originals, but you lose some degree of flexibility.
Supose you decide the guitars may sound better at 70% pan instead of 100%(I'm guilty of wide mixes, but I am not a big fan of hard panning). Or you may want to give the guitars slightly different EQ to help differentiate them. This is difficult if they are already locked into a stereo track.
However, if your original mono tracks are available, and you effectively use your busses, everything exists in a relatively fluid state. You have more complete control, and the flexibility is really nice as you work toward that final mix.
Just my 2c