Now-a-days everything we work on is FOSS, and for almost all of our history the major products we've had also were FOSS. You could even call up SUSE in the old days and ask for a CD with all of the source code for SLES without being a customer. These days you can download all the SLES sources from OBS (it's what openSUSE Leap is based on), and SLES has a Factory-first policy that requires all new changes to first be sent into openSUSE. All of our products (to my knowledge) are FOSS licensed and we provide the source code for all of them as source RPMs -- even if they aren't copyleft -- and on GitHub in most cases.

I would very much argue that Red Hat and SUSE can easily trade blows on which is the "more open" company in this regard. For instance, SLES sources are far easier to get access to and work with than RHEL sources in my experience (and our kernel sources are actually separate patches rather than a single patch blob). But that really doesn't matter at the end of the day -- we both work diligently on free software and contribute upstream consistently. Canonical I'm not as sure about, but from my experience collaborating with them they also do an absolutely immense amount of upstream work. In the past, they were quite sheltered and didn't contribute back, but this changed significantly many years ago.

[I work at SUSE, and all of my work is upstream and free software work. I've never touched nor seen a single piece of proprietary code in my 3 years of working here.]