Ok, so you have a midi file. You can import that into Sonar and load up a soft synth with the sound that you want it to play.
You want to record your voice singing along to the midi file. What type of microphone do you have and how are you connecting to your computer?
I don't quite understand what you mean by "tonality plus 1 (velocity) or minus 1."
So in simple steps:
1) import the midi file into sonar and route it to a soft synth with the sound you want it to play.
2) Create a new audio track to record your voice into. Set the input to your microphone.
3) Arm the track and press record. The midi file will play and you can record your voice along with it.
Hope that helps.