The
Steps to Justice website has some terrific and trustworthy legal information about your situation.
The section dealing with evictions for renovations starts here:
https://stepstojustice.ca/questions/housing-law/can-my-landlord-make-me-move-out-repairs-or-renovations/but the part that addresses your specific question about preserving your right to return is here:
https://stepstojustice.ca/steps/housing-law/protect-your-right-move-back-later/So I believe you only need to send your landlord a letter (probably best to send it registered mail) declaring your intention to ustilise your right to return, and your new address (if you have it at that point). And keep your landlord updated in writing with regards to your address while you are out of the building. You should probably speak with a lawyer to make-sure that this is done right, and that no details are missed.
I believe that the law requires the landlord to
provide a similar apartment (similar square footrage and facilities, etc.) while allowing for some changes, as the renovations may be quite significant (i.e., your exact apartment may no longer exist following the renovations). But you would be better to ask a lawyer about this.
With regards to the rent, they are only allowed to charge the rent that you
would have been paying, if you hadn't been temporarily evicted. So, for example, if while you are out of your apartment, you would have received your annual rent increase, then the landlord is allowed to include that rent increase in your new rent. So your rent stays the same as it would have been, not exactly the same as it was the day you move out. Again, you should probably check with a lawyer.