You didn't mention which version of sonar your using and which version you were using that had the Time/Pitch stretch plug in. If its still installed on your PC you may still possibly have access to it through the plug in manager.
TBH, this plug in was generic. I used it Pro Audio 9 and back in the day it was generic but it did what it should.
Todays standards are a little different. This plug in is almost 15 years old.
As previously mentioned, try slip stretching, Autosnap or probably your best bet is to use Melodyne.
But then again, I have no idea what version you are using, so all my suggestions are generic.