I am a Canadian expat in the Middle East who went through the trouble of hiring an experienced international tax lawyer from a major law firm to make sure our last tax return, and separation from Canada, was bulletproof.
I hate to be the bearer of bad news, but being considered a 'Canadian tax resident' is not linked at all with physical residency. Being deemed a tax resident is linked with having enough ties back to Canada or demonstrating the intent of coming back. Spending more than half a year in Canada (this also dictates provincial taxes, which is all or nothing: a full year or none) certainly ticks both. However, even if you spend an entire fiscal year abroad, CRA can still deem you a tax resident owing the exact same amount of taxes to CRA as if you had worked in Canada (minus the difference paid in your country of residence, which in my case is el zippo). To add insult to injury, there is no actual expat tax code to follow, you can only go with prior court cases. But say you kept your Canadian professional membership, rented your house to your sister at below fair market value, kept all your bank and credit accounts, and contributed to your registered retirement plan: you will be deemed tax resident by CRA, no doubt about it.