Live in Ontario, Canada. I am seriously considering moving to another
town for career reasons. The move may not happen right away. Could
take up to 10 months from now. I have an interested party who would
like to buy the house now. Since it will be an investment property and
not their main residence, they have agreed to let me rent and stay in
the house in the meantime. My question is: What if this opportunity
falls apart and I decide I would like to buy the house back? This
interested party would not give me any problems about changing my
mind. They are very supportive. Is this legal?

I can only guess for Ontario. In The USA IRS = Internal revenue does
not like people to do such things, but, I think it is ilegal only if
you attempt to reduce your taxes. An audit is likely if the IRS
computer detects (unlikely) you repurchased the same house, but you
should pass the audit unless you cheated.   Neil