Preference center setup w/out subscription groups?

It can be argued that a 1-click unsub is required (including by gmail earlier this year), as a result of that, you should have the 1-click header option enabled already.

You can create your own unsub page, alternately, can setup a user attribute and set that attribute each time a user is added / removed from a subscription group (if that is what you want to use).

For the targeting, you can setup an audience which uses the subscription group and use that in your canvas or campaign (no real difference between that and using a group though).