Being less than 183 days in one taxation year is not a reason for changing the status to "non-resident". According to Canada Revenue Agency if someone has BOTH following conditions, he or she will be considered as "Non-Resident" for tax purposes":
- Having no ties to Canada
AND
- Staying in Canada less than 183 days in one taxation year
So if you had enough ties to Canada in 2012 (PR, home in Canada, health card, etc.), automatically you are considered resident for tax purposes even if you were in Canada less than 183 days.
Also based on definition of Canada Revenue Agency, the immigrants make the ties from their date of arrival to Canada.
You can check website of CRA for more description about this subject (definition of resident for tax purposes, ties, etc.)