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.