Other than making selections, opening the Clip tab of the Inspector, changing tempos, etc., it
is just a couple clicks. Things always sound more complicated when described step by step. You can simplify it further by using the shortcut to bring up the Audiosnap Palette (mine's non-default so I didn't mention it) and clicking the Clip Follows Project button there which automatically enables Audiosnap at the same time. That makes it one keystroke and one click to get Autostretch enabled on all selected clips.
But I'll give you the need for more flexible tempo and pitch control; The thing that's surprisingly difficult to do in SONAR is to stretch audio
without preserving pitch.