The CCRA has a few publications about this, but in the end they look at the whole picture. Some people get spooked into thinking that residency and citizenship are the same thing-- they are not. Becoming a non-resident of Canada is not synonymous with a renounciation of Canadian citizenship.
One issue that is a strong tie of Canadian residency is if you are still on your Provincial Medical Plan-- lets face it, it's an expensive social project in Canada and you are expected to pay. Just turn it in, it isn't worth the money anyhow, and if some day you decide to go back to Canada you can get it again with a 3-month waiting period. Canadian drivers licences are another strong indication of residency, since, (duh), residency in Canada is a condition of their issuance and they are a proof of residency.
I recommend consulting with an attorney who specializes in Tax Law. A few years ago I hired one, his fee was about $1500 for the consultation. He assessed my entire situation, and made helpful recommendations. In the end, it was a large fee, but worthwhile and a drop in the bucket compared to what I would be paying with an unpleasant surprise down the road.
CCRA also has a form where you fill out your particulars. You send it in, they assess it, and right away they tell you if you are considered a resident or not for taxation purposes. I recommend doing this even if you go through a lawyer, since then you have a backup record.