From the MNR site:
"If you are an Ontario resident between 18 and 65 years of age and you want to fish in Ontario right away, you can buy a "Resident Temporary Fishing Licence and Outdoors Card and Application" from one of more than 1,800 licence issuers across the province. This temporary paper licence is effective immediately and valid until December 31 of the year in which it was purchased. The fee for a temporary paper licence includes the cost of a three-year plastic Outdoors Card."
For the full details go here:
http://www.mnr.gov.on.ca/en/Business/LetsFish/2ColumnSubPage/STEL02_164832.html
I personally have never bought a licence in The Park, I think you can, just not sure where.
You can buy a licence at any Canadian Tire store, they are all over the place.
Mark Rubino
Mark's Algonquin Park Sampler - Blog
Mark's Algonquin Park Sampler
http://www.ABRweb.ca .. Algonquin Backcountry Recreationalists - Caring for Algonquin's Backcountry