Yes, SUSE CaaS Platform 2 can usually be upgraded in place to version 3.

However the 3-to-4 upgrade has significant architectural changes and will be a disruptive one, and we recommend standing up a new cluster and migrating workloads.

So it's your decision whether to go from v2 to v3 now, and do the disruptive migration later, or wait and go directly from v2 to v4 via the disruptive upgrade.