Having lived in Europe and the US, you are a visitor for Canadian customs purposes. This is not a bad thing as you are not subject to the same import rules as other Candians returning from vacation. Just put down that you are a visitor and show your Canadian passport. They'll ask why you are abroad and how long you are staying in Canada. Not really a big deal as you cannot be denied entry into your own country. The only time that it matters is when you are returning home for good. There are duty exemptions that can be claimed for goods purchased while living abroad. I will admit that it is weird to see a V on the customs form for your own country but you will get used to it.