Can I force python3's os.walk to visit directories in alphabetical order? how?

Yes. You sort dirs in the loop.

def main_work_subdirs(gl):
    for root, dirs, files in os.walk(gl['pwd']):
        dirs.sort()
        if root == gl['pwd']:
            for d2i in dirs:
                print(d2i)

I know this has already been answered but I wanted to add one little detail and adding more than a single line of code in the comments is wonky.

In addition to wanting the directories sorted I also wanted the files sorted so that my iteration through "gl" was consistent and predictable. To do this one more sort was required:

for root, dirs, files in os.walk(gl['pwd']):
  dirs.sort()
  for filename in sorted(files):
    print(os.path.join(root, filename))

And, with benefit of learning more about Python, a different (better) way:

from pathlib import Path
# Directories, per original question.
[print(p) for p in sorted(Path(gl['pwd']).glob('**/*')) if p.is_dir()]
# Files, like I usually need.
[print(p) for p in sorted(Path(gl['pwd']).glob('**/*')) if p.is_file()]