Update: May 1st, 2014 - Looks like things are doing better than expected, so the date has been moved up to May 6th. Hope to see you out there!
“Due to substantial ice depths and lingering signs of winter in Algonquin Park, backcountry permits will not be issued until May 9, 2014. This includes permits for allranger cabins and overnight backpacking trails. In addition, all campgrounds in Algonquin Park (except Mew Lake) are also expected to remain closed until May 9, 2014. Mew Lake Campground, normally open year-round will remain open. Full refunds will apply for current reservations. No penalty fees will be incurred for modifying arrival dates. All visitors with reservations through May 8, 2014 will be alerted by telephone."
This includes overnight backpacking, however day-use of the hiking trails is ok.