Similar, here is the notation in new features
http://www.cakewalk.com/Documentation?product=SONAR%20X3&language=3&help=NewFeatures.27.html
I believe it does more than the old option maybe something to do with VST3 handling.
 
The doc still shows the X2 preferences dialog image BTW.

Hello.  I am reporting back.
1) I DO NOT hear reverb tails at the beginning of tracks made by bouncing other tracks that play thru the Breverb.  This is good (IMO), because I don't want to hear any effect tail at the beginning of any tracks
 
2) If I go to Edit/Preferences/Audio/Playback and Recording and dis-able "Play Effect Tails After Stopping", I get no reverb tails when stopping playback in the middle of a track, but I do get the reverb tail when re-starting playback a measure or two before the beginning of the track. (It's as if the reverb tail that is not played when playback is stopped, and is instead played when playback resumes - even if that playback is resuming before the start of the song.)  If I enable "Play Effect Tails After Stopping", I hear the reverb tail when I stop playback in the middle of a track, but I do not hear the ghostly reverb tail when re-starting playback a measure or two before the beginning of the track.  The way those reverb tails are handled is a little strange, IMO.

BbAltered
2) If I go to Edit/Preferences/Audio/Playback and Recording and dis-able "Play Effect Tails After Stopping", I get no reverb tails when stopping playback in the middle of a track, but I do get the reverb tail when re-starting playback a measure or two before the beginning of the track. (It's as if the reverb tail that is not played when playback is stopped, and is instead played when playback resumes - even if that playback is resuming before the start of the song.)  If I enable "Play Effect Tails After Stopping", I hear the reverb tail when I stop playback in the middle of a track, but I do not hear the ghostly reverb tail when re-starting playback a measure or two before the beginning of the track.  The way those reverb tails are handled is a little strange, IMO.

I dunno, seems logical to me. If you disable "Play Effect Tails After Stopping," this stops whatever is in the buffer from playing back when you stop. Audio doesn't just leak out of the buffer, so when you press play, it kicks back in. If you enable "Play Effect Tails After Stopping," then the buffer gets a chance to flush after you press stop. So when you press play again, you start fresh. At least that's how I think it works, maybe scook can confirm.

It works as documented. If SONAR can cause plug-ins to "play effect tails after stopping" what might be useful is another option to flush effect buffers silently after stopping. Maybe this could be added to the new "Always Stream Audio Through FX" parameter. I don't think much can be done for X2a.

In any case, I have figured out how to stop those reverb tails from appearing before the actual start of the song.  This is helpful because I have listeners (i.e. the "talent") hearing those reverb tails at the very start of playback, who then want to know what is wrong with my computer or software!!

What I do is fairly simple - just make sure your project 'end' includes the reverb tails.
 
You can do this in a variety of ways:

1. Insert a marker
2. Slip edit any clip to encompass the tail
3. Edit any automation node to encompass the tail

There are other ways, but these are ones I would consider using.

This used to bug me too.  Now, before I bounce to tracks or create a premaster, I just place the cursor past the end of the song and play 2 seconds of silence.  Then when I go to the beginning of the song to bounce, there is no residual reverb tail.