In most cases, your Landlord is required to give you at least 24 hours notice to enter. There are however some exceptions. They are as per Section 26 of the Residential Tenancies Act 2006, S.O. 2006, c.17; which reads as follows;
Entry without notice
Entry without notice, emergency, consent
26 (1) A landlord may enter a rental unit at any time without written notice,
(a) in cases of
(b) if the tenant consents to the entry at the time of entry. 2006, c. 17, s. 26 (1).
(2) A landlord may enter a rental unit without written notice to clean it if the tenancy agreement requires the landlord to clean the rental unit at regular intervals and,
(a) the landlord
enters the unit at the times specified in the tenancy agreement; or
(b) if no times are specified, the landlord enters the unit between the hours of 8AM and 8PM 2006, c. 17, s. 26 (2).
Entry to show rental unit to prospective tenants
(3) A landlord may enter the rental unit without written notice to show the unit to prospective tenants if,
(a) the landlord and tenant have agreed that the tenancy will be terminated or one of them has given notice of termination to the other;
(b) the landlord enters the unit between the hours of 8AM and 8PM; and
(c) before entering, the landlord informs or makes a reasonable effort to inform the tenant of the intention to do so. 2006, c. 17, s. 26 (3).
So be careful in bringing any harassment type of application against your landlord for not providing notice, as notice may not be required!!