If your name was on the deed, it would be a fairly simple capital gains transaction.  If there was a partnership agreement in place detailing the loan and the expect split of profits from a sale, it would be a simple capital gains transaction.  With nothing in place, I expect that if  there was no documentation of the loan at the time, it would have been considered to be a non-taxable gift from father to son.  Now when your son reports the sale of the residence, if his was the only name on the deed, he will be the only one reporting the entire capital gain. Your return of $77,000 might be considered a non-taxable gift from son to father.  I suggest you both see an accountant to discuss the situation and get some advice.

Per CRA: You may have a capital gain or capital loss when you sell or transfer capital property. Some common types of capital property include land, buildings, shares, bonds, fund and trust units.