From an Irish viewpoint you'll be entitled to the split year treatment. This means that you will get a full years tax credits in Ireland and rate bands as you will be considered to have moved your residency to Canada in Sep 2019. If your sole source of income is from your employment (Irish/Canadian) you should not have any additional Irish tax liability on your Canadian income and you should be able to obtain your tax refund as calculated.
You'll need to be abroad for a full 12 months in order to get the split year treatment so you may be required to wait a while before you get your refund. I'm not 100% sure what the Revenue practice in this area is.