Yes, absolutely. It has to be based on household income. A unit that costs 50% of the market price can be said to be affordable, but if the rent doubles, the household occupants would no longer be able to pay it because their income would not have doubled. A unit that costs no more than 30% of the household's income is therefore an adequate target.
As for long-term affordability, I believe that the owners must not be profit-oriented. That's an important condition. Otherwise, in the private sector, over time, sale is inevitable due to the lure of capital gains.
The last thing I want to point out is that, over time, non-profit organizations with large real estate stocks build the equity needed to refinance their mortgages and repay their debts. They thus financialize the housing, but to build long-term affordable housing, not to make a profit. For sure, there's currently a short-term crisis. However, in 15 or 20 years, those property owners will have been able to repay their debts and, as in the private sector, build and purchase housing units, renovate existing units and develop their real estate stock. That's something that's been greatly neglected in Canada. Projects are carried out, but the owners aren't taken into consideration.