Hi everyone!
I just phoned the CRA to ask some questions, and I actually got a reply that I wasn't expecting: I'm most likely considered a non-resident for tax purposes and therefore shouldn't file a return!
This came up because my first question was that I'm unsure if I'm an ordinary/factual resident, or a deemed resident. I told him that I'm living in the US completing a PhD and all of my income sources are US, and he said that 4+ years is not considered a temporary absence, and that I'm almost definitely a non-resident, period. He suggested that if I want an official ruling, I should file an NR73 and see what the response is, but he reiterated that there's no way I'm not a non-resident. He sounded pretty sure.
I then went and did some reading about it (see http://www.cra-arc.gc.ca/tx/tchncl/ncmtx/fls/s5/f1/s5-f1-c1-eng.html ), and while it's complicated, it generally sounded from the wording there that at the end of the day I would be considered a non-resident, as my ties to Canada are only in the form of my parents who I visit once a year, and there's absolutely no certainty about whether or not I will return to Canada after my PhD.
So, this would suggest that for many other people in this thread they would also be non-residents and don't have to bother with this entire exercise?
But I read somewhere that even though I'm a non-resident, I can still get the tuition tax credits (and in particular won't have to pay taxes on this "scholarship income")...