Hi Zarmas,
This article might help you clarify what you're legally allowed to do.
https://medium.com/real-estate-simp...landlord-increase-a-tenants-rent-c671ce4f112e
Unfortunately, you cannot increase rent to any desired amount for existing tenants, regardless if there rent is well below market value. However, there many be a way to slightly increase the rent by applying for a rent above guideline increase - in order to apply for the above guideline increase, one of the following circumstances must apply to you (see article for details).
If the tenant has agreed to an increase, ensure you get this in writing. Technically, if the tenant becomes aware in the future that it's not permitted by law, they could come after you for being over charged on the bases that they were not aware of their rights.
Beaware that The Landlord and Tenant Board is becoming even more strict on landlords and more favourable towards tenant rights (as they've always been).
As for the above advice to sign a new lease - in Canada, leases automatically roll over regardless of whether a new lease in signed. For our units, we have tenants sign a year lease and yet still are not allowed to increase rent using a new lease. If someone else has experience with increasing rent via. new leases for existing tenants - i'd love to hear if it's possible! That'd be great news. However, it's always been my understanding that due to the nature of leases rolling over - using a new lease to increase rent is not allowed - as the tenant doesn't have to sign a new lease to stay in the apartment.