Aunt, uncle, wife and I got Moderna after AZ as well. Pretty much if you got AZ as the 1st shot, you will get Moderna as the 2nd shot (provided you didn't go to a pharmacy to a second dose of AZ).
Thinking they are saving Pfizer for those who received them as a 1st shot and for the children (since Pfizer is still the only approved vaccine for children in Canada)