finalizing a song

Everything you need is in there.
 
Although many of us prefer third-party tools (e.g. iZotope Ozone) for mastering, it's actually quite feasible to do it all using only bundled tools. Some are conventional VST plugins and some are ProChannel modules (which are really just SONAR-specific plugins).
 
There are four primary components used in mastering: EQ, compression, limiting and analysis. All are adequately covered, although I'd recommend adding at least one third-party component, the free Voxengo SPAN, to augment the fourth category.
 
For equalization, in the mastering stage you're usually after subtle corrections. That means mostly cuts rather than boosts, mostly of 3 dB or less, gentle slopes (except for subsonics removal) and broad ranges, and often linear-phase equalizers. The ProChannel EQ works fine for this, but the linear-phase EQ (LP EQ) is, IMO, easier to use. There are a gazillion third-party options, e.g. the very popular FabFilter Pro-Q2, but I think LP EQ is perfectly adequate.
 
Compression in mastering is also subtle, what's often referred to as "glue". That mostly means gently raising quiet parts for greater volume consistency, kind of smudging all the mix elements into a whole. Although there are several popular third-party compressors (one of the most popular is actually named "The Glue"), the ProChannel compressor does this quite well. 
 
SONAR provides several limiters (Boost11, BT Brickwall, BT Limiter) but I personally can't comment on them as I've had limited experience with them. I'm sure others here will offer their expert opinions.

I think I have seen templates in SPlat for mastering, which presumably have the plugins loaded. Not tried them though.