Those Terrazas share some tech with the Chevy Uplanders which led me to this forum post by someone after a Google search for ‘2007 Buick Terraza Van intermittent cruise’.
https://chevroletforum.com/forum/uplander-31/cruise-control-turns-itself-off-2007-uplander-61121/
Check the post by ‘in2pro’ as it references a technical bulletin a dealer would use to diagnose an issue with cruise. In short, you can try a couple things:
1. Try the break pedal position with your foot in an ‘up’ position ( may be a pain in the butt to do ). Possible it will prevent the break switch from disengaging cruise.
2. Check your stop lamp assemblies. Remove the bulbs, clean the sockets and bulb bases, put them back in. This is a bit easier to check and doesn’t require a trip to a mechanic.
