As of July 2020 plane travel between Alberta and Ontario is permitted and there is no mandatory quarantine policy. Having said that, each province finds itself in its own unique situation, and a new quarantine policy or new lockdown would prevent John E. Marriott from being able to attend HOWL.
Although it is much more likely for John E. Marriott to attend HOWL in person, there is still a possibility that his role in the convention may be limited to presenting virtually via Zoom, similar to Melissa. If you are disappointed that John E. Marriott might present virtually, then you have by September 15, 2020, to cancel and get a full refund of your ticket.