There is no limit on how many times and for how long you can extend your stay as long as you have proof of personal financial support and the reason for doing so, in this case again - family class sponsorship - people want to be with their loved ones while waiting for PR, for some it takes less than a year, for some it takes 2 or 3+ years.
Good for you regarding your multiple citizenship
, but I don't see how this relates to the topic. You are aware though that many countries do not allow dual citizenship? Not sure where you are coming from, but you may be liable for a crime and fraud right now, I sure hope CBSA will check you out thoroughly.
Good luck