In case it helps anyone: My sales rep told me I could set up my employees in QBO and then migrate my data.  This was a mistake.  You cannot add any payroll data to QBO before migrating.  The migration will stall without any explanation as to why.  It took four days of phone reps working with me before the issue came up.  It should be the first thing they ask you when your migration fails.  It had nothing to do with the Dropbox or Google Drive, just data in the new QBO file.