Would you consider just handling activate for windows directly in the lib/venv/__init__.py method "install_scripts(self, context, path)"
https://github.com/python/cpython/blob/4f98f465f14e7258c5b18a62c5aa114dbe1174d8/Lib/venv/__init__.py#L382

    if not srcfile.endswith(('.exe', '.pdb')):

        # handle activate for Windows (ignore WSL)
        if srcfile == "activate":
            # from docs: on unix drive is always empty
            d, p = os.path.splitdrive(context.env_dir)
            d = d.replace(':', '')
            p = p.replace('\\', '/')
            if d:
                p = '/' + d + p
            data = data.decode('utf-8')
            data = data.replace('__VENV_DIR__', p)
            data = data.encode('utf-8')

        try:
            data = data.decode('utf-8')
            data = self.replace_variables(data, context)
            data = data.encode('utf-8')
        except UnicodeError as e:

IMHO I don't think the use of windows python in WSL is a realistic use-case, my preference would be to just make this fail. In fact I tried to use it, and I could not make it work.
1. /mnt/c/path/to/python -m venv venv
Error: [WinError 5] Access is denied: 'C:\\WINDOWS\\system32\\venv'
2. /mnt/c/path/to/python -m venv -m venv /mnt/c/some/path/to/venv
fails silently, appears to do nothing, venv is not created
3. /mnt/c/path/to/python -m venv -m venv 'C:/some/path/to/venv'
makes directories at C:\some\path\to\venv, but can't be activated in WSL, that I can figure out
source /mnt/c/some/path/to/venv/Scripts/activate
: command not found
-bash: /mnt/c/some/path/to/venv/Scripts/activate: line 4: syntax error near unexpected token `$'{\r''
'bash: /mnt/c/some/path/to/venv/Scripts/activate: line 4: `deactivate () {

I guess I don't really understand why it would be useful to use the windows python in WSL, and if that's the only thing holding a quick fix for this, I guess, I would prefer to just handle windows python in windows in git-bash, and ignore WSL. Would you be open to that?

If so, I'm happy to submit a PR

thanks!