Segregating a public internet over our corp network

I'm guessing this is totally achievable, just looking for ideas on the best implementation. So a little background first:

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Headquarters: We have a Sonicwall NSA 2650 with 200mb symmetrical from our ISP. Cisco 3750E as our core switch

CoLocation (down the street): Cisco 3750-X (core) They connect back to us over a comcast business EPL circuit

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Diagram here:https://imgur.com/a/rJy7LNk

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The public internet we have at the remote office is currently off a different ISP, segmented from our CORP network. People just use it to stream music, surf the web on lunch, etc. Its only 3MB down though, and we can't get anything else into the building. So since we have a 200MB pipe going between both sites, we want to use that maybe. Obviously theres a security issue since it would ride on the corp network.

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I'm looking for ways on how to set this up from a network perspective. My initial thought was to keep the UNIFI on the same vlan I have it on now, but give it an SVI since it doesnt have one. I could make it 10.18.2.0 or something. Then I'd have to build that vlan at headquarters too and on the sonicwall. Then I'd make another SVI (vlan 91) and route the traffic over that vlan? Then I'd have to do some sonicwall magic to block traffic to and from that network. Any ideas?