Like you found out from the OFSC, trails are a no go with snow bikes. You need to go where the backcountry sled guys ride. In Ontario Wawa is the popular backcountry riding area. Others go to the chic-choc mountains in Quebec and Upper peninsula in Michigan.
You can play around with the crown land atlas to try and find some rideable crown land closer then those 3 places I suggested. It's not easy to use but there are some youtube videos around that explain how to find what your looking for. Not all crown land allows motorized vehicles.
Geocortex Viewer for HTML5
The compound in Muskoka (think Bracebridge area) is a snocross practice track that I believe they allow snowbikes to ride on.