We're a SaaS company and originally had our guides at https://www.example.com/guides/<guide name>. We eventually moved from there to Freshdesk and have our guides at https://support.example.com. We re-created all of our existing content there.

However - we never created canonicals on our original guides or redirected our old guides to the new. And our old guides now rank REALLY well for a lot of long tail and even some great short tail stuff. We get over 50% of our traffic due to these old guides.

Unfortunately, they are old and not maintained, and we don't want to maintain guides in two places. So we have a few choices and I'm not sure which one will result in minimizing traffic losses. I'd love your thoughts.

Permanent redirect from each old guide to the new guide.
Canonical pointing at the new guide and a message at the top of the old guide saying "This guide is no longer updated. Please see the newest version at <link here>".
Keep the old page but put a message at the top saying it's no longer updated and you'll be automatically redirected, and then after 5 seconds redirect to the new guide.

I'm open to other ideas too.