YYCNoob,
I prefer to do it as one Return ticket because I never used 2 separate one-way ticket to enter any country.
Air Canada website:
After I highlighted the eUpgrade button, I selected Latitude on my first flight.
On the second flight, I tried to de-highlight the eUpgrade button; I got the following message: "To make change to eUpgrade, please return to the first flight in our itinerary. "
It seems that the Aeroplan system not allow me to do eUpgrade on my first flight, while no eUpgrade on my last flight.
I don't know how to do it in one ticket.
Thanks!