Salesforce Integration with Constant Contact, 2-way sync

We use Constant Contact for email marketing. We have used it for several years and have a mailing list of over 30k contacts. We recently changed CRM to Salesforce Professional Cloud and would like to keep contacts synced between the two platforms. 

I want a 2-way synch, so any changes to a contact in either platform are synced to the other. From what I have read, Constant Contact’s Salesforce connector is one-way from Salesforce to Constant Contact.

Does anybody have experience with a solution or a 3rd party connector?