Wow, you do have a lot of questions...

US*G is a good thing to start with since it gives you lounge access on all *A flights except on pure domestic USA itineraries. Have you looked at US' program at all to determine if there are useful benefits for you besides lounge access? Their new Envoy (business class) seats are pretty nice so maybe there are some ways to grab a confirmed TATL upgrade even if that means a connection through FRA/MUC/ZRH/LHR etc. Within the USA you would get a spot on the upgrade list anyway from the unlimited domestic upgrade program.

Regarding AC, I do like their Executive First seat (business class) and the nonstop to YYZ where you can do US pre-clearance is convenient. You can infact use miles to upgrade, AC participates in the *A upgrade scheme. However these seats come out of the award bucket and are generally limited to 2 on each flight, so they are gone very quickly. The better way to upgrade though is through their eUpgrade credits you already mentioned, these can only be used by AC Top Tier members. Once you reach at least 25K status miles, including a minimum of 5 flights or 10K on AC aircraft, you get Prestige status the following year (instant recognition starts at 35K) and can start using the credits. If you buy a flexible fare, AC calls these "Latitude", you can get a confirmed upgrade at time of booking if R class is available. Not sure how much a Latitude CPH-YYZ-MCO return is but CPH is one if the cheapest points to start from within Europe.

Have a look at the Miles & Privileges section on aircanada.com.