It is possible, but there is a good amount of setup and development needed. You'll also need Marketo Enterprise Edition, because it requires setting up separate Lead Partitions. SFDC would be integrated natively, and it would be linked to 1 Lead Partition. Dynamics would be integrated via middleware that uses the Marketo SOAP API, and it would sync to the other partition. Contact services@marketo.com if you'd like a quote.