I was going to say this is a good task for a wave editor.
Wavosaur is free, and Gold Wave has a demo that is an honor system and is only $40. Wave lab Elements is very powerful and only $90. Wave lab is faster with mouse editing than Sound Forge,, less clicks to do the same task. 

artturner
Thanks to all for your comments. It was the audio zero crossing issue that I had to learn more about and deal with. Ultimately, after trying to fix it within Sonar for a day or so, I finally gave in and downloaded the SoundForge Pro trial and fixed it in about 2 minutes.
 
Thanks again!

I'm curious, what did you need to do in Sound Forge to get the loop working the way you wanted? I'm trying to think of a function Sound Forge has that would make it possible whereas it wasn't possible in Sonar. I have and use Sound Forge, but I use Sonar all the time to make loops.
 
The only time I HAVE to use a wave editor is looping the sustain in notes for sample libraries. Unfortunately in Sound Forge, the loop points are not always recognized by SFZ players - it's a known bug that has existed for a while. Wavelab doesn't have this problem, but I find it harder to hit the right loop points than with Sound Forge. So I create the loop points in Sound Forge, then bring into Wavelab (which recognizes the loop points), then save from Wavelab.

For some reason, I was really struggling to find the zero crossings in Sonar. Even with snap enabled, it didn't seem to be giving me the results I wanted. Since I had heard so many people talking about using SoundForge, I decided to give it a try. I was just impressed that the first time I touched the software it did exactly what I needed. It snapped to zero crossings and I shaved a little of the beginning and the end. And suddenly I had a seamless loop.
 
Like you said, it didn't bring any new functionality to the table, it just seemed to work better, or at least more intuitively. 

IMHO Sound Forge is very underrated because it doesn't have a fancy UI, but its functionality and ease of use is really quite something.
 
I wrote an article on Sound Forge tips and tricks for harmonycentral.com, but it hasn't been published yet. You might want to watch for it...