You qualify for the Northern Residents Deduction if you lived on a permanent basis in a prescribed zone for a continuous period of at least six months. This means you must "maintain a dwelling" there and be able to provide proof if CRA requests supporting documents. 

Here is what CRA says about maintaining a dwelling: A dwelling means a self-contained domestic establishment. Generally, this is a complete and separate living unit with a kitchen, bathroom, sleeping facilities, and its own private access. It includes a house, apartment, mobile home, or other similar place of residence in which a person usually sleeps and eats. It does not include a bunkhouse, dormitory, hotel room, or room in a boarding house. We consider you to have maintained and lived in a dwelling, even if your employer let you live there rent-free and paid all the utility, maintenance, and other costs related to the dwelling. Each person living in the dwelling can claim the basic residency amount as a deduction on their return. However, if more than one person claims the basic residency amount for a particular period and dwelling, no one in that household can claim the additional residency amount for that period and dwelling.