Adding User ID to Hubspot cookie


In Our company (VELUX) we would like to bridge HubSpot data with Google Analytics, for this reason I would need to add user ID in to cookies, I know that HubSpot implement hubspotutk on successful CTA completion but what I am asking is a cookie that keep user ID (seven digit unique ID) . I would appreciate to have you suggestion about this and as well the best practice to bridge GA and Hubspot analytics together.