Powers of attorney are governed by provincial law, so I can speak only for BC. It is not only legally possible but common for elderly people in BC to grant an "enduring power of attorney" that remains valid as long as the grantor is alive, even if they become completely incompetent; it ensures that somebody, usually a trusted family member, will be able to take care of the grantor's property. There is no power of attorney that becomes invalid when the grantor is asleep.

In general, an accused person's criminal record is inadmissible at trial; so is any other evidence intended to be used to show a propensity to commit the crime alleged. A convicted person's record is, of course, admissible and VERY relevant at sentencing.