Can someone object to my probate application in Ontario?

Yes, a beneficiary can file a Notice of Objection. If a beneficiary has filed a Notice of Objection (Form 75.1), the applicant must give notice to the objector using Form 75.3. If an issue needs a judge, a judge reviews the application and may make an order. What happens next depends on the issue raised.

Probate is the court procedure for giving someone authority to act as estate trustee, confirming a named trustee's authority, or approving a will as valid, and the document issued is a Certificate of Appointment of Estate Trustee. Land registry staff accept that certificate as proof of an estate trustee's authority over a deceased owner's land. That is why the timing of a challenge matters.

If a dispute goes to court, the court may appoint an administrator while an action is pending about the validity of a will, or to obtain, recall or revoke a probate or grant of administration. That person, called an estate trustee during litigation, has general powers except distributing the residue and is under the court's direct control. Estate litigation documents are filed through Civil Submissions Online, not the probate email process. A lawyer can explain how disputes like yours generally proceed.