In my iOS 7 app, I detected if a segue was a popover via this check in prepareForSegue:
if ([segue isKindOfClass:[UIStoryboardPopoverSegue class]])
Elaborating on Joey's answer, which led me to what seems the new manner of achieving what we used to do with UIPopoverController.
This code in prepareForSegue:Sender:
UIViewController *destination = segue.destinationViewController;
UIPopoverPresentationController *ppc = destination.popoverPresentationController;
ppc.delegate = self;
is a simple way to successfully set your view controller as delegate of a UIPopoverPresentationController much the same as you are probably used to doing with the old UIPopoverController.
And, of course, while you are at it you'll probably add:
[destination setPreferredContentSize:CGSizeMake(300.00f, 300.00f)];
if you were in the habit of setting UIPopoverController size here as well.