Set "Show subscription plans at registration" to "No" in CBSubs > Settings > Global then use the normal display plans URL. Specifically the below URL (can also be a menu item via menutype Community Builder > Plugin).
index.php?option=com_comprofiler&view=pluginclass&plugin=cbpaidsubscriptions&do=displayplans
If not logged in it'll just show the registration page. If logged in it'll show the plans selection page. You'll probably also want to set "Suggestion text for plans subscription (always displayed)" to empty in CBSubs > Settings > Display > Plans.
By doing this they will not be able to select plans during the registration process. They will need to register, login, and then can subscribe to plans. If you want plans as part of the registration process, but on 2 separate pages then there's no solution for that as it's a single form and it cannot be broken up into multiple pages. You however could use tabbed or step by step registration layout in CB > Configuration > Registration.