^^ Definitely make use of lead in/lead out time. Those parts will get scrapped in a final product but allow for synching. A visual transient (exaggerated gesture while playing so you can find the "best single frame" for the attack) can be married to the attack of the sound.
 
The "two sources" can also potentially (and probably) result in drift for playback as well, so a second "transient" at the end is also useful to create. It is easier to stretch audio between two video transients (use markers to easily find those two frames), but I am not familiar with your version of SONAR so not sure how to do this "step-by-step." Aligning the first transient, and then stretching the audio to the second marker is the most universal method used. You may also need to bounce/render the audio to get the best result of any stretching used.

Again, I am not "recording" anything WITH Sonar, I WAS merely trying to sync audio and video from two other sources USING Sonar LE, which came bundled with the new DAW.  
 
I will not be doing so anymore, because I have found Sonar LE to be absolutely incomprehensible and completely useless; the icons are positively microscopic, and it didn't come with a simple "straightforward text plus illustrations" instruction manual.  (Instead, it only offers a bunch of YouTube "instructional videos," which is a bloody stupid way to do business.)    
 
Again, I used to be able to do this VERY easily with my old DAW (Boss BR 1180-CD), my sports action camcorder and Windows Movie Maker, but the old DAW died; I wanted to get the next one in the series (Boss BR 1200) but it was no longer available in any "brick and mortar" stores, and I can't shop online.  
 
That's how I found myself stuck with the Boss BR 800 instead, and it is proving EXTREMELY difficult to find the EXACT start time for the camcorder so that the two recordings will match up.  (I also absolutely HATE the BR 800's "touch-sensitive controls.")
 
No, I can't perform a "sharp sudden movement" because my hands are already full; I only have two hands, after all, one of which is needed on the DAW and the other is needed on the camcorder.
 
Once again, I will not be using Sonar for several very good reasons, not least of which because it did not come with a proper (straightforward text plus illustration) instruction manual.
 
So again, thanks very much, but just drop it already.  
 

The solution is very simple and was laid out clearly.  There is no reason to spend lots of money for new software, all of which will work the same.  I think what the confusion is, you don't realize that you can trim the start time of your audio and slid it back to line it up with your video
 
If you decide not to give up, feel free to PM me and I can help you

Mac Leahy
The "audio clap" won't be audible on the video because the microphone on the camcorder is a dud, and there won't be any "audio clap" on the DAW because I'm recording an instrument, not vocals.  I can't do instruments/vocals at the same time.  (Or at least not without sacrificing that most sacred of all aspects of music..."tone.")  

You don't have to hear the clap on the video....just "see" the frame where the hands meet.  That is how the "clap board" works.  The audio mixer finds the clap and puts it in the frame where the top stripe makes full contact with the bottom half.  Has been done that way for over 75 years. 

Mac Leahy
Again, I am not "recording" anything WITH Sonar, I WAS merely trying to sync audio and video from two other sources USING Sonar LE, which came bundled with the new DAW.  
 ......   
No, I can't perform a "sharp sudden movement" because my hands are already full; I only have two hands, after all, one of which is needed on the DAW and the other is needed on the camcorder.
 
So again, thanks very much, but just drop it already.  
 

I suppose I don't even understand what you're actually trying to do. If you're not recording anything with Sonar, what is it that you're trying to sync? Combining audio and video from two external sources while theyre being recorded simultaneously in real time? I think your job description is incomplete to say the least??
 
There is a 1800 page Reference Guide pdf for SONAR to download, but as LE is a cut down version that is not sold separately, there is no manual for that specifically. That means the reference guide includes material that doesn't exist in LE-version, which can be confusing´/irritating.

It sounds to me that he is trying to do in camera editing. If that is the case, and using different sources, he is always going to have issues.