I am not an immigration lawyer. Something you should be aware of is that when applying for a green card, your status as a Canadian (whether permanent resident or citizen) or as a Brit (ditto) is completely irrelevant. The green card process sees your application solely through the lens of your birth country. The GC backlog for Chinese-born people is very lengthy. So lengthy that it tests the longevity of a visa or a set of visas -- it's not a marathon you want to still be running 15 to 20 years from now.
For that reason, if your goal is ultimately the US, focus on the US, because you will otherwise be adding _many_ years to the process.
One very notable asterisk to the above: If, while applying for a GC, your spouse is from a no-backlog country (born in Canada, UK, or other no-backlog countries), then your application can essentially adopt that country as the birth country, and you can get through the GC process in a relatively short time (all other things equal).
From your perspective "good timing for a green card application" is ASA-F'ing-P.
Yes, HK is treated as its own country for chargeability purposes, which AFAIK has never been subject to additional delays. Macau is treated as part of Portugal, so it will also never have limitations.
Both of those are specifically provided by Congress as exceptions to the general rule of charging to the current sovereign of the place of birth.
Correct. Hong Kong is the correct country of chargeability so the process, particularly if an NIW-based green card is pursued, would be around two years based on current green card backlogs and processing times. The problem with TN status for those pursuing green cards is that because of the current backlogs, you might be in the difficult position of needing to travel or extend your TN while you are in the green card process but bot far enough along such that could get temporary travel authorization. You would not be able to travel or extend your TN.
For that reason, if your goal is ultimately the US, focus on the US, because you will otherwise be adding _many_ years to the process.
One very notable asterisk to the above: If, while applying for a GC, your spouse is from a no-backlog country (born in Canada, UK, or other no-backlog countries), then your application can essentially adopt that country as the birth country, and you can get through the GC process in a relatively short time (all other things equal).
From your perspective "good timing for a green card application" is ASA-F'ing-P.