From the official Quetico Provincial Park Facebook:
Please be patient with us and the late spring ice off.
Our Cache Bay, Prairie Portage, Lac La Croix and Beaverhouse Entry Stations do not have internet connections at this time and cannot modify backcountry reservations, issue fishing licences or process payments.
If you have a backcountry reservation at one of these entry stations between May 19th and 24th please pre-pay your permit in full online (https://reservations.ontarioparks.com ) or by phone (1-888-668-7275) before you arrive and bring a copy of your confirmation letter to the entry station when you check in with a park ranger. Impacted reservations will be called directly by a park ranger.
Dawson Trail Entry Station and Campground, and Atikokan Entry Station have internet and will operate normally.