I will believe that CCleaner installs Avast after the fact and on its own the first time I encounter it, and not before.
I've got 5 machines in my household, and on 4 of them CCleaner is assiduously kept up to date. I have not yet had it do anything unexpected and there is no business that would be insane enough to risk alienating a massive user base, and creating a PR nightmare, by "deciding for you" after an installation that something else entirely needs to be installed.
I haven't had a bit of trouble with Google Backup & Sync, either.
Brian - Windows 10 Home, 64-Bit, Version 1803, Build 17134
A little kindness from person to person is better than a vast love for all humankind.
~ Richard Dehmel