First of all, the crime of "Theft by a person holding power of attorney" is a specific crime under section 331 of the Canada Criminal Code. It is considered a specialized form of theft, which is a crime against property. The attorney can be found to have committed this crime if he or she sells, mortgages, pledges or in any other way disposes of some or all of the person's real or personal property. It is also theft if the attorney sold or mortgaged the property legitimately but then kept the proceeds, or did anything at all with the proceeds that he or she was not authorized to do by the Power of Attorney document. So you can see that it's a pretty broad definition.
The thieving Attorney can do jail time, as the punishment is the same as any other kind of theft. If the value of the property stolen is under $5,000, the jail term can be up to two years. If the property is worth more than $5,000, or if the property stolen is a testamentary instrument (e.g. a Will or Codicil), the jail time can be up to 10 years.
The reason many dishonest attorneys get away with abusing their position under the Enduring Power of Attorney is that nobody notices what's going on. And if anyone does notice, they tend not to say anything because they are too polite or feel they don't know enough about it, or they simply don't want to look greedy or nosy.