Maybe not the right section so move freely if not.
I keep getting emails from people from avcanada about multi time but some of them don't include a return email address or phone number and its sent from webmaster@avcanada.ca so theres no way of responding back. Is there a way to find out the senders information or email address?

On this page, the very top left says "0 new messages" (0 being the number that you have, whatever it is)

Click on it, it will take you to your inbox and you can reply direct from here

If you are getting emails forwarded through the AvCanada system, the reply address should be set to the sender of the message, and not AvCanada.