This F0 tornado was reported by witnesses who saw it touch down near Earlton in Northeast Ontario, but no damage was found. Given the remote region in which the touchdown occurred, and a lack of damage surveys in the area, it is possible that damage occurred through forested area, but went undocumented.
Figure 1 depicts the surface observations at 2:00 pm EDT, which shows a cold front slicing through northern Quebec/Ontario with a warm/moist environment ahead of it. A thunderstorm (marked as “R”) was also ongoing in northern Ontario. This thunderstorm possibly tracked east-southeast and eventually might have been responsible for this F0 tornado.

According to Environment and Climate Change Canada (2018), an F0 tornado touched down at 3:20 pm EDT near Earlton, ON. The path and width of the tornado was not documented by ECCC. The tornado caused no fatalities, injuries or property damage.
Sources
NWS Weather Prediction Center Surface Analysis Archive. (2017). Surface analysis 18Z Wed Jun 25 2003. Retrieved from: https://www.wpc.ncep.noaa.gov/archives/web_pages/sfc/sfc_archive.php
Environment and Climate Change Canada Data. (2018). Canadian National Tornado Database: Verified Events (1980-2009) – Public. Retrieved from: http://donnees.ec.gc.ca/data/weather/products/canadian-national-tornado-database-verified-events-1980-2009-public/