This is using
BiabVST and
ReaTrak to choose from the thousands of session players instruments and drums to add track/s to your own session.
In the demo video we are fitting a guitar solo in this case starting at bar 17 to 24, the bars were highlighted and the 7 solos generated.
To preview the solos in sync to my existing tracks I select one track at a time in the VST setting it to play along with the Reaper tracks, I do this until I find a solo that fits best then simply drag it into Reaper (it has a 1 bar buffer at each end to allow for pick-up notes and tail notes.
The yellow icons on the right are the MIDI notation (RealCharts) that can also be dragged in.
Watch
https://www.dropbox.com/s/4dqm8awxjp...iriff.mp4?dl=0
Download
https://www.dropbox.com/s/4dqm8awxjp...iriff.mp4?dl=1