Each Province has its own rules for residential tenancy.

You need to figure out what the law is governing rent increases in your jurisdiction, then follow it.

I am not trying to sound snotty when I say this, but that is what you need to do.

Here in Saskatchewan, if the tenant is on a month to month basis all you need to do is give them 3 months notice of the rental increase.

Secondly, market the crap out of your vacant units and show them a lot! Don't be lazy, make sure you really push them. This building will bleed cash until you fill those vacancies. Everything else can wait until that task is finished