What you can do
Sync New and Modified Subscribers from MailChimp to Hubspot
Sync New Contacts in Hubspot to MailChimp
Sync only Specific type of contacts/subscribers using the Filters app
check more possibilities to integrate MailChimp and Hubspot.
What you can't
Copy existing MailChimp subscribers to Hubspot, or vice-versa can't be done. Bots only deal with New data. You can do a one time CSV file import / export for this - these docs can help. MailChimp - import & Export; Hubspot - Export & Import
Tracking Email open and Click activity in MailChimp and syncing it with Hubspot isn't possible
Limitations
Hubspot's New Contact trigger pulls a maximum of 100 contacts every 5 minutes