I'm not sure if this is the correct forum to put this in or not. Anyway, I used a very old version of Music Creator to play MIDI files and control my Vocalist Harmonizer for spot harmonies. Works great. Now I want to know if I can use MP3 backing tracks and sync with MIDI somehow instead of having to play the MIDI files. I want to be able to import the MP3 and still use MIDI to toggle the harmonizer on and off for the spot harmonies. Can this be done and what product should I use? I would appreciate any assistance.

Hi. I do not have MC, so unsure about MP3 support. But if you click on File, Import, Audio and select an audio file / MP3, does it import the file?
If it doesn't support MP3, you could use a free audio converter (just Google free audio converter).
All the best.

If Music creator doesn't work, Home studio will certainly do what you wish. I'm working on a similar set up. 
I have used WAVE ( could be MP3) files for 13 years now played back from a laptop ( or Netbook) and I use win amp and a foot controller. I love the system and it has never failed me. But I miss having midi control my vocal and guitar effects like I used to do back in my Atari sequenced live midi days. I guess I could also purchase a harmonizer! :) 
 
So I bought HS and will try the playlist function.  
Because I already have 150+ backing tracks mixed to stereo I will start with dragging those to a Sonar CWP project and then adding a midi track to control to my effects. So I will start with most songs only being 3 tracks. Stereo out and a midi out. 
 
As I have time I am also re doing my tracks and those will be available as 4 track output. I mostly want to separate my Bass to a small bass amp and I might use a small sub to enhance my kick.  The rest can stay stereo. 
I have no desire to be mixing channels live when I play but bass is something that is venue sensitive.  
 
I will bounce or freeze all my synths so I'll only use audio.