PJH
I've been requesting time stretching multiple tracks at once for about 6 years now.

Found something: Find out how much you want to stretch by ctrl-shift drag. Make note of the amount, 105% for example, and then select all the tracks you want to stretch. Go to 'Process' - 'Length' and perform the stretch there. Works well!

Thanks for that. Another little piece of Sonar to learn. Interesting that it also includes a formant adjuster.
 
A more intuitive way is in order for multiple track stretching as this one is rather crude and will require a lot of experimenting. So far my attempts aren't yielding desired results - tracks aren't stretching at the same rate as they should be.
 
At this point if I want to stretch multiple tracks I'll do them individually or mix them down to a single track and stretch that one.