Nope... my initial post was right.
What I meant was if you are a UA Premier Exec (equivalent to AC E but you need to fly 50K Q miles) or UA 1K, you will earn 100% bonus miles for all UA metal flights.
The advantage of Aeroplan is that all Q miles that you earn from Star Alliance carriers (AC, UA, MX...) will count towards getting those 10K threshold bonus for every 10K Q miles.
If you are going to fly mostly UA, then MP is good for you. If you are flying AC and putting points into MP, then you'll get a lot less points than putting them into Aeroplan.
Sounds alright now?