That's odd. Are you not seeing a subscribe button at all (on lemmy.ca) when you go to the !cats community or are you clicking the button and nothing happens?
In regard to the other instances, you should be seeing a message in the sidebar of each cat community that states "You are not logged in, but you can subscribe...To do this, paste the following into the search field of your instance: [email protected]". You should be able to copy the !cats address, paste it into the search box on lemmy.ca (which is where you are logged in), click the search button, and the community should appear with a Subscribe button.
If you don't see subscribe buttons at all then you may have to complete the config file fix linked to by @[email protected]