Traveling to Toronto for ASLH?

Are you not a Canadian citizen and planning to attend the annual meeting of the American Society for Legal History in Toronto next month?  ASLH Treasurer Craig Klafter has just sent the following message to preregistrants:

All non-Canadian citizens require a passport to enter Canada. US citizens do not require a visa, but other nationals may require one.  If you require a visa, please contact the Treasurer as treasurer@aslh.net to secure an invitation letter and Canada Border Services letter. Visa-exempt foreign nationals need an Electronic Travel Authorization (eTA) to fly to or transit through Canada. Exceptions include U.S. citizens and travelers with a valid Canadian visa. Please check with the Canadian Embassy or High Commission in your country of residence.