Can a beneficiary ask the court to replace an executor who is stealing from the estate in Alberta?

This answer covers the law of Alberta.

Generally, yes: Alberta's guidance says you or your lawyer may apply to the Court if a personal representative is not complying with their duties. If satisfied, the Court of King's Bench can order them to perform a duty or core task, impose conditions, remove them, revoke the grant or make another order it considers appropriate. Removal is an option, not an automatic result, so the Court may choose a lesser remedy.

An executor must act honestly and in good faith, in line with the will, and with the care of a person of ordinary prudence. Taking estate money for personal use would raise serious questions under those duties. If no grant has issued yet, anyone may apply to restrain dealing with the deceased's property, and a caveat lasts 3 months unless the Court orders otherwise. Once a grant has issued, beneficiaries cannot simply agree to replace the executor; a change needs a court order or the executor's renunciation or resignation as the court permits.

Good records help. A person interested in the estate can apply for an accounting at any time, and Alberta's guidance is to try discussion before going to court. A lawyer can tell you how to gather evidence and whether to apply.