I think at this point the best that can be done is
- put up a type of “we’re moving” message on the com site
- if the site has users subscribed to a “newsletter” include the information in that.
I would advise to not send out emails to every email address you may have if they have not opted-in to getting emails. It might be that only the com domain would be at risk of getting blacklisted as an email spam site, but I don’t know if some blacklisting ignores the TLD in which case the ca domain would be in trouble too.
Other than that, it will take time for users to search and find the new site.