cloudHQ can be used to sync Dropbox and Google Drive accounts.
This means that Dropbox and Google Drive accounts will be the exact mirror of each other.

Single user sync:

If you are looking to sync just one Dropbox account, then you just need to create a two-way sync pair between Dropbox account and Google Drive account. The main limitations of that approach are that sharing metadata will not sync’d.

The instructions how to migrate a single Dropbox account to Google Drive are here

Sync multiple users:

If you are an admin of Dropbox Business domain and G Suite then cloudHQ sync all your Dropbox accounts with corresponding Google Drive accounts. All sharing metadata will be in sync too. Instructions how to sync your Dropbox Business installation with G Suite are here

How do I transfer files from Google docs to Dropbox? So the purpose of this support note is sync between Dropbox or Google docs..