Hi Neil,
Because you are so limited in how much you  can raise rents in Ontario, I would raise it every year by the amount that is allowed unless you personally feel there is a good reason not to.  I would do this with a good letter explaining why you are increasing, such as the fact that cost of energy is up by X% which is more than what Ontario allows you to raise.  In most cases, the increase allowed by the province is always less than inflation.  One of my 2 triplexes is severly under market rents because the previous owner never raise the rents.  Now, I can only raise the rent by the 1.8% or whatever they choose each year.  Essentially I can never get market rent until I get that tenant out. I have to bite the bullet until they move out(not likely as they know where ever they go, they will pay 50% more rent).
If you don`t raise rent every year, then as the costs to manage, heat, maintain goes up each year, your cashflow goes down.  Use other incentives to reward good tenants, like a 50$ gift card at Wal-mart, gift baskets, thank you letters, cards etc
There are always exceptions and it`s great to have the ability to make them.  That great tenant that wants to stay in that suite for "ever" increases your cashflow in the sense that you don`t have to factor in the vacancy rate.  Good topic Neil, I can`t wait to see what others reply.
Real