Sonar X3: creating realistic sounding strings

What are some ways to create realistic sounding strings in Sonar X3?   I may have a need - I wanted to use a real quartet for a recording project, but it's looking like that might not work out. So I have come up with a Plan B.    I assume it would involve MIDI strings and some kind of synth manipulation in Sonar.   I'll likely be importing a MIDI source file of strings from Finale 2014.
 
I'm using Sonar X3 in a Windows 7/64 environment.

I have some large string libraries and they sound great if you do as Dan suggested and add keyswitches to switch articulations as needed.  This can be a little painstaking but it works.  These libraries are also expensive.
 
You can sort of fake that with a keyboard that has good string sounds (MOTIF, TYROS 2 and higher, etc.).  In those cases, you may needed separate tracks for the various articulations: one track with legato strings; second track using a different patch with staccato sounds, etc.  If you are lucky, you will only need two or three articulations in a song.  If all the lines are legato, then you are really in luck and it sound be easy.  High-end keyboards have really good samples.
 
Also, realistic voicing is important.  String parts are usually (but not always) spread out instead of all being clumped together like piano chords.  Good string parts also (usually) have moving lines and not just sustained chords (and from your post, I think you know all that).  One thing that makes strings sound fake is when the player uses a string patch that has a slow attack, and then quantizes so the notes start right on the beat—which ends up making them all sound late.  Everyone will immediately hear that.  You may need to nudge you parts left so that the slow attach starts a little before the beat, making the full sound coincide with the beat.
 
If you do take the plunge on a library, I highly recommend Vienna over others.  It is far easier to use—but any string library needs a fast hard drive that isn't too full, and preferably an SSD.
 
If you have the full Kontakt version, you might look at Sampleism.  I just bought their violins and considering how inexpensive they were, they sound great.  Well, in fact, they sound great no matter what—they just don't have as many features as a big library.  I didn't look to see if they have the other strings.
 
One personal note:  I have had great luck getting string sections and full orchestras, but have always had trouble getting a string quartet to sound right.  Not sure why.
 
 
 
 

An easier (maybe even cheaper) solution you might want to consider is hiring someone like Konrad ( ck out fifteen minutes of fame at http://www.themightykonrad.com/ ) to do them for you.

I found the Sonar Dimensions Pro strings nice.
Or maybe this free one:
http://www.vst4free.com/index.php?plug-ins=Strings
 
Here there's more free string VST's (there's 5 pages of them..)
http://www.vst4free.com/index.php?plug-ins=Strings
 
good luck