A will (signed by an attorney or otherwise) does not confer any automatic rights to beneficiaries upon your passing. It would still need to pass through a probate process in the respective jurisdictions where you hold assets that require distribution.
So if you have a will which designates beneficiaries of either all your assets (e.g. 50% of everything goes to XXX, 50% to YYY) - or specifically itemises assets ("property XXX goes to YYY")... this will go through the probate court in Hong Kong, and only after you receive the probate document (assume entire process to take 6 months), only then can you deal with the title deeds of your property.
Having your will drafted by an attorney would add credibility, and they would of course ensure it's properly worded. However ultimately it's up to the court to determine its legitimacy and validity, produce the probate grant accordingly. In theory you can write your will on a piece of toilet paper, signed by two witnesses, and it would be equally valid. Thus you could do this from Canada, or your next holiday to Azerbaijan. However, be prepared to expect scrutiny over its legitimacy.
Similarly with PoA... this can be done from overseas. The PoA ordinance makes no explicit provision for documents drafted abroad (nor does it forbid this), but common convention is that documents written in an accepted language are OK - although it may help to find a HK-qualified notary, or otherwise apostille of the PoA signed by your local lawyer. For specific requirements you should check with the entity that requires the PoE: for example banks in HK would have a list of criteria you must fulfil for an overseas PoA.