Using 7-zip portable in a GPL app

7-Zip is released under the LGPL with unRAR restriction: http://www.7-zip.org/license.txt
The PortableApps launcher is released under the GPL: https://portableapps.com/apps/utilities/7-zip_portable

Depending on how you're using 7-Zip Portable, you may be able to bundle it with a commercial application; if you're actually linking to it in the code you're writing (instead of invoking 7-Zip Portable, sending it some parameters, and letting it do its thing) however it will need to be under the GPL.

If you don't need your users to use the 7-Zip GUI, however, it may be easier to do what the team behind AppCompactor did by bundling just 7za.exe, the stand-alone 7-Zip command-line client: http://www.7-zip.org/download.html
This program, like the 7-Zip GUI version, is licensed under the LGPL with unRAR restriction, so you can use it regardless of the license for your project.

The unRAR restriction prohibits people from using the freely-available but not freely-modifiable unRAR source code from the Roshals to reverse-engineer a way to create RAR files and thereby compete with RARlab's own WinRAR and command-line RAR products; this is why there are plenty of open-source products that can read RAR files but none that can make them.