I’ve done this just now for opera-developer, opera-beta and opera. I tested that auto-connect is happening correctly with:
$ snap interfaces opera-developer
Slot Plug
chromium-ffmpeg:chromium-ffmpeg-93464 opera-developer
...
gnome-3-28-1804:gnome-3-28-1804 opera-developer
gtk-common-themes:gtk-3-themes opera-developer
gtk-common-themes:icon-themes opera-developer
gtk-common-themes:sound-themes opera-developer
...
$ snap interfaces opera-beta
Slot Plug
chromium-ffmpeg:chromium-ffmpeg-93464 opera-beta
...
gnome-3-28-1804:gnome-3-28-1804 opera-beta
gtk-common-themes:gtk-3-themes opera-beta
gtk-common-themes:icon-themes opera-beta
gtk-common-themes:sound-themes opera-beta
...
$ snap interfaces opera
Slot Plug
chromium-ffmpeg:chromium-ffmpeg-93464 opera
...
gnome-3-28-1804:gnome-3-28-1804 opera
gtk-common-themes:gtk-3-themes opera
gtk-common-themes:icon-themes opera
gtk-common-themes:sound-themes opera
...
I noticed that opera didn’t pass automated review due to it adding the dbus interface, and granted a snap declaration for that as well.