In Ontario's real estate contracts, offers to lease a property normally have an irrevocable date and time. Irrevocable is defined as incapable of being recalled or revoked.

In order words, it means that an applicant invites landlord to enter into a rental contract which is unchangeable and unalterable by the applicant within the irrevocable time.

Usually the irrevocable time for landlord to consider applicant's offer is 24 hours.

Therefore, applicant should only submit one offer to one property within the irrevocable time because you are binding for signing such an offer. 

No overlapping of irrevocable time for more than one offer made by the applicant even more than one property you like. Making multiple offers will / may cause you to be responsible for entering into multiple rental contracts.