Q: What is the maximum upload file size for iCloud?

Hi ..

You can upload any file size as long as there's enough iCloud storage available.

Open System Preferences > iCloud

Storage available at the bottom of that pane.

For iCloud Drive (right now only available with iOS 8) there is a file size limit of 15 GB.

You can store any type of file in iCloud Drive, as long as it's less than 15 GB in size.

See: iCloud Drive FAQ