Networks

Hi, so I've got a scenario that I'd love to get some feedback from network engineers out there.(linksyssmartwifinet).
We have a mission-critical application that needs to be set up in a colo where multiple outside companies would need to access that environment securely. The connection needs to be available 24/7/365 in a high availability setup.
One suggestion is to set up using a router(s) in the colo where these "client" networks would create a tunnel into. Another suggestion is to go with firewalls at the colo. Now, these spoke offices don't know each other and don't need to know about their respective networks. Their main concern is to be able to reach the main network in the colo, securely and to make sure the speed/performance is excellent.