I've never heard of a December monarch sighting in Toronto but I was in Niagara Falls in early Dec of 2001(?) for a 2 night stay and saw a monarch on Dec 5. The trip, with a group, was planned weeks earlier and we REALLY lucked in with the weather, temp 18C, people in shorts and tees, etc.! Probably should have reported it to somebody but it didn't occur to me at the time. Monarchs have been seen at Point Pelee in Dec but such sightings ARE extremely rare.