With regard to making midi sound real, one of the things I have been trying to get to is the ability to differentiate between (for instance) a flute moving from one note to the next by maintaining breath and changing fingering (legato) as opposed to tonguing from one note to the next, or the difference between a violin changing fingering during the same bow stroke as opposed to using a fresh bow stroke.
 
Notes played on the keyboard have basically the same attack.  Is there a function in Sonar to remove the attack on notes? Years ago I used to do this in Pro Audio 9 using a CAL to basically take a whole note and change the pitch to turn it into a group of notes played legato.  I can't find that CAL anymore and I don't even know if it would work in Platinum.

 
Following this thread :  How Do You Do A Midi Slide?,
it looks like the CAL script you want is called Slur.cal
 
which can be found in the "CAL" download from Mike V. (mudgel)    [taken from this thread :  CAL files. Enjoy! ] :
 
https://onedrive.live.com/?cid=df413f5445183b18&id=DF413F5445183B18!105
 

I read this with interest and thought I would throw another thought into the mix. Before I do though, I want to qualify that I'm aware you probably aready know most of this. I am coming from a basic level for those who are just starting.
 
Midi never makes a sound...so to say I need to know how to make midi sound good is only part of the picture. I think I know what you mean't by that...but I'm simply clarifying...the other half of the picture is sound library quality and included articulations. I can have the best midi in the world, but if my samples aren't very good or I don't have recorded articulations to play all I can do is attempt to emulate some kind of a fix in midi programming, and it can be done to a fairly acceptable level, but I would always want good included articulations, high quality samples and maybe round robin capability. I might also try to augment with real strings if at all possible....lots of decent players in community orchestras who might help you out for a few bucks! 
 
Hollywood strings, Albion...Orchestra Runs...Kirk Hunter...check these out, but be ready to pay for good samples. Some of these programs come pre panned and ready to go.

Most hollywood composers required to create midi scores for television productions tend to augment with real musician or two.  Usually a soloist where midi falls flat.  
 
If you are stuck with MIDI only.  Follow the advice of Hanz Zimmer:  Compose for the sounds you have, don't pretend they are the real thing.  It is a major limitation, but it is preferable writing something idiomatic for an instrument that cannot be reproduced convincingly.  
 
If you need to do a little faking.  Consider slightly overlapping the cutoffs of string parts into the next note, unless it is a repetition of the same note, the connection will seem much more convincing.   

Jerrylan9638
 
Notes played on the keyboard have basically the same attack.  Is there a function in Sonar to remove the attack on notes?

You're too late - it's closing the barn door after the horses have left. 
 
You don't say what sound source the MIDI is driving.  For synths, patches can do things with legato mode to maintain existing envelope positioning when changing to a new note.  For samplers, good (read expensive) libraries will articulations to control attack, among other things. 
 
In theory, one could do some stuff with pitch bend to continue a line of notes in a legato fashion - but, man, what a headache to program it!  And it would likely sound fake much of the time in any case.

Interesting comments, guys. Paul P, Thanks for the lead on the CAL
dmbaer, your comment on pitch bend is actually what that cal I was mentioning does programatically
 
In the midi specification there is a "pedal" or controller (68) which is supposed to remove the attack phase and play the notes in a legato fashion.  I have not been able to get it to work in the VST synths I have in SONAR Platinum.