Actually using Sound Forge to Master is a much better choice. Sonar lacks a wave editor and measuring tools needed to zero in on your peaks and overs. Although it contains most of the tools, their implementation is clunky compared to Sound Forge or Wave Lab. With wave lab I can "See" where peaks are and quickly reduce the gain. This can be on a microscopic level. You can also analyze for RMS average output which is essential if you want all your songs playing at the same volume on an album.
The peak level meter alone is worth the price of the software. I'm sure Sound Forge works the same.
The CD burning and MP3 conversion is also well designed in a wave editing program.
Sonar is my Multi track tape deck, MIDI sequencer.
Wave Lab is my 2 track tape deck, CD/ MP3 burner.