Nobody monitors our movements into/out of Canada. We are not that important! If one is returning to Canada after a long gap (this info we provide on the customs form we fill when entering Canada), immigration officer would, at the most, make you aware of the fact that you could lose your PR if you don't fulfill residency requirement. We should stay in Canada for more than 730 days in first five year period and should be in a position to prove that. It is better to stay for more than 3 years, apply for the citizenship, and be relieved of stay duration worries.