Mastering A Final Mix In Sonar

Well the short answer is yes, you can absolutely master in Sonar.  I do it all the time.  The deeper answer has to do with your knowledge of the tools at hand.  There are enough tools in the packaged version of Platinum to master a song effectively. 

  Not to start a thirty page argument here, but this sounds like a chance to check out that L&R thing so many were bent out of shape about.
   SPLAT has the tools to do what you want to do, but mastering a mix takes practice. Mastering takes professional dedication. Of course the only way to get any experience is to do it. So...
   The new LP Multi-band compressor is a fantastic tool. You certainly can do the job with it. Just try not to get too heavy handed. The LPEQ is also very nice (I'm tempted to use all 20 bands on something just to do it).
   The CD your friend gave you is an opportunity to learn a new skill. Dive in the deep end and swim.

Just for something quick and easy...try putting the VC 64 plug on the master bus....select the Master Mix preset from the pull down menu and see what it sounds like...you can tweek the settings in there too...might be a place to start
It adds some EQ and compression
 

I know that LANDR seems to spark controversy here but have you tried their demo? That may be all that track needs. I don't personally use LANDR, I use Ozone. Have fun mastering!

LANDR is an automated mastering service

You can do mastering in SONAR. All the essential tools are there: EQ, multiband compression, limiting. I'm pretty sure there's even some plug-ins for exciting, imaging, and tape simulation. The only things really lacking are EQ curve matching and LUFS metering, but you can live without those, especially if you have a reference track that's close to the overall sound you want.
 
I use SONAR with a couple of instances of Ozone 7 in the master FX bin, saved as a template. This makes it easier to get some sonic unity in a project with multiple songs. I tend to import one mix at a time as a stereo track starting with a "standard" set of Ozone module settings, then tweak the Ozone modules for the individual songs.
 
I am by no means an authority on this, but I've learned a lot from reading and watching videos on mastering, and even more by trial and error. For me, the most important rules are 1) don't overdo anything, and especially 2) don't be reluctant to go back to the mixing stage if mastering reveals mix problems. Once you have tracked and mixed a tune, you're often sick of it and ready to be finished. Don't give into the temptation to try to master a mix that needs fixing.