If I understand correctly, RSVP permission (rsvp_event) is meant to be used, to act on behalf of user.
I'd like to provide UI with buttons to state decision about event, however I don't require the application to do it for user, user should make the decision.
Is it possible to provide Dialog to Attend/Maybe/Decline event, without having the RSVP permission in App, in similar manner to Like button or Friends invite Apprequest?
If it's important, I'm using Canvas with application written only for this purpose, not on distant website or anything.
This is of course not possible. Even with the rsvp_event permission you always have to let the user decide, you are not allowed to do that stuff in the background.
Your App is on Canvas, but it´s not Facebook, it´s your own App. Without the permission, users can only use the official Facebook functionality.
Just a heads up btw, rsvp_event needs to get reviewed by Facebook if you want to use it for non-admins. See changelog: https://developers.facebook.com/docs/apps/changelog