You will be limited by the road plowing that takes place, or doesn't, at the access points in Algonquin. There aren't many backcountry access points that are accessible in the winter, if any.
Take a look at these articles found on the Algonquin website:
Winter in Algonquin Park
Winter Permits & Information
Did you check out the trip reports under the "winter" tab here on AA?
Here's another winter trip report, which starts at Access #1:
Please take note that the Big Pines Trail and Parking Lot is closed October 15, 2013 to Spring 2014