There are two different questions here.
1. Secure Connect DC IP addresses- We utilize the Umbrella DCs so we use the same public IP addresses as Umbrella when connecting via IPsec tunnels. You can see the Umbrella DCs and their IP addresses here. Note no all Umbrella DCs support Secure Connect, check the Secure Connect DC list here.
2. The public IP that will be listed as the source when landing at a destination such as a SaaS application will be one of the IPs in the Umbrella ranges. 146.112.0.0/16, 155.190.0.0/16, 151.186.0.0/16. We are just launching Reserved IP as a function in Secure Connect which will allow a customer to purchase dedicated IP addresses, more details to come on the Reserved IP capabilities.