If flying business class is important to you, then I suggest that for the second ticket to redeem only YVR-YYZ-YVR in business class.

Then you can buy a seperate ticket in business class using $$$ for YYZ-MIA-YYZ.

I don't know if you can do this, but perhaps you can do the YYZ-MIA portion on United Airlines (UA) (in First class on a 2-class aircraft, which is treated as "business class" for Aeroplan purposes)?

Also, since you are flying to MIA have you tried checking to see if there is award availability for First Class (on a 2-class aircraft) from YVR-MIA on UA? You can try various hubs such as DEN, ORD etc.