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Who determines if you are "Resident of Canada for tax purposes" or Not ? Does an individual have to file an application to CRA for it ?
 
Thanks for your reply , should i fill the tax portion for 3 or 4 years ?

You have to fill your tax portion for all years in the relevant period.

Under the old rules that is six years, unless you became a PR less than six years go.

Under the old rules that will be five years, no matter when you became a PR.