We're moving a client from Pardot to Marketo, and they'd like to know if they can use the same CNAME they've been using for their Pardot landing pages for Marketo LPs - "go.companyname.com". There will be about a two month overlap where they will have both Marketo active (for set up) and Pardot running until our hard cutover from one system to the other. I think the answer is no, but wanted to confirm that before I mis-speak with the client. Thank you!
It is not possible to have the same CNAME point to two different servers.
The only way it's possible to serve pages from 2 different origins via the same hostname is if you point the CNAME to a CDN (or, generally speaking, a reverse proxy) and enforce a naming convention so a URL is explicitly tied to one server or the other, e.g. Marketo pages always start with mk_.