Would love to know how you guys engage Sonar to get your creative juice flowing..
Does any additional cakewalk product or other software help with that?

My guitar or a lyric (or both) starts the whole process.
 
To me SONAR is (in the end) a big ol' tape recorder that MIDI syncs to soft synths and has an unlimited rack of "outboard" gear.
 
I try to keep it simple.
 
For me, it's rare that a piece of gear (or be it a synth or FX) gets my juices flowing.
 

It's more of how to setup Sonar (or any DAW/HW) to NOT get in the way of the creative process. Two items that have helped from a songwriting perspective;
 
1. Templates (audio tracks for recording guitar/bass/vocals, midi tracks for piano/drums)
2. Groove clips (basic rhythm concepts for song parts and easily shifting/copying to quickly block out an arrangement)
 
Everything is pretty much setup to just flip a switch, tune and plug in. 

To me SONAR has nothing to do with the actual creative part of the process. It's all acoustic guitar & a pencil.
The guitar solos or horn section parts I record singing/humming them and imitating this with the keyboard. 

I get musical ideas that pop in my head all the time.  If driving, I grab my cell phone and turn on video recording, and simply sing the idea into the phone - it requires no hands away from driving to do, so not a safety issue.  I then transfer that to the computer at first opportunity, then will play something into Sonar quickly just to capture that little snippet.
 
I do the above many times a day, and have a growing army of little bitty 'snippet' projects.
 
I will periodically cruise through those snippet projects, and will then flesh them out, a bit at a time, based on that little melody or rhythm that I first started with.
 
It appears my steering wheel is quite the percussive instrument, using palms, fingers, keys, whatevers.
 
As far as using Sonar directly for song writing, I generally have some sort of idea in mind when I am actually going to set up a project in Sonar, so I start by loading whatever sorts of instruments I 'know' I am hearing for a particular song, and then also load up one of many drum 'track templates' I have, for the kind of kit that I hear in my head for what I am about to capture.
 
I usually get the meter changes in place first, as I tend to write prog tunes that have multiple meter changes - measures of 4/4, 5/4, 7/8, 9/8, 11/8, 13/16, 19/16 - lots of interchanging sections.  These I always set up first, so that I don't have to mess around with all of that stuff after recording tracks.
 
Then, I normally lay down some sort of 'placeholder' tracks - usually some kind of keyboard pad sound, but sometimes bass, which I do just so I have something to play against, and then I will use various instruments to 'play around' a given section, so that what is being played is done over some marginal structure - I like to write parts for different instruments so that they are not competing for the same frequency ranges, so that each instrument can be heard.  For ME, keeping some sort of backing sound helps me to keep the 'real' parts more sparse, but still able to hear a semi-full part.
 
I then sort of run a concept through whatever its logical/emotional conclusion is, and then get a clean 'break', and come at it again laterm with an eye/ear to develop in a new direction - sometimes complimentary, sometimes as counterpoint, just depends on the mood - how much coffee - donuts, etc.
 
Sometimes, I take a listen through snippets I have already created, as sometimes one or more of those can be a real interesting insertion into a new project - giving me a direction that would not have likely come from trying to think of a part right there on the spot.  That's the beauty of having snippets.  Lots of folks have done that sort of thing over the decades - for me, that works well.
 
So, at the end of it all, Sonar is a big scratch pad, with LOTS of really nice ways to build things, save them off, recall them, and then shape them into something that somehow all flows together.  It's the BEST recording software program for matching how MY brain approaches creating music, and that is why I have used Sonar for well over 20 years.
 
Bob Bone

Typically it's merely a matter of just hitting record as I usually "come in" with an idea (be it melody or progression). Other times I just let things fly and noodle around for something to inspire a new project or not.  However, just the other day I had an idea which I was tweaking Z3ta+ 2 for an atmospheric backdrop with a busy percussion ticking away while the lead guitar would sing some dynamic rhythmic melody on top.  So, it did take me some time to get the desired sound from the synth and sketch out some drum patterns until I actually recorded anything.  Most of the time, I just record the idea in the rough and then work from there to perfect and flesh it out.  At least that would be the way for my own recordings.  As for recording someone else or a group, that is a much more involved process more or less.
 
Kind regards,
 
Living Room Rocker

...and then get a clean 'break', and come at it again laterm with an eye/ear to develop in a new direction - sometimes complimentary, sometimes as counterpoint, just depends on the mood - how much coffee - donuts, etc.
 
Man am I glad I wasn't taking a sip of hot coffee when I read that!!!

You could do worse than fire up one of the hundreds of free drum loops which come with Sonar and just jam along with guitar and keyboard. Sometimes this inspires me to come up with a riff or chord pattern. That's all I need as the "seed." Later you can of course replace the loops with your own drum parts.

Since I'm not much of a player, SONAR (or analog back when) is integral to my songwriting process.  I find a rhythmic riff on the keyboard, or step-sequencer, or loop I like and, in the case of the riff, play with it until I have a some sort of progression.  Lately it has been bass.  Then I build the song up from that, layering on, McDuff.  Drums lately have been coming from  Heavyocity, which lets you play loops across the keyboard (with velocity), which helps soften the drum machine effect, and often takes the song in a different direction.  My technique, such as it is, involves throwing everything up on a sonic rhythmic wall and seeing what sticks.  Without the recording aspect, I couldn't work the way I do.
 
I leave the melody stuff to the singer and now guitarist, who take the song even farther done the road.  The song I'm working on presently was pretty much EDM until the guitar part.  We finally found a chugging rhythm counter point that turned it more to rock.  What is funny is he was using more of a David Bowie/Mott the Hoople guitar sound (distorted but spare), which I never really liked all that much, but it really works for this song.
 
So I've used tape, or midi & tape, or P5 or SONAR to write.  SONAR is just the most invisible process for me.
 
@