r_swift

The last two times I have flown out of Pearson with my EAD/AP, they held me in secondary. No questions, nothing like that, but literally held me until my plane was DEPARTING in 5 minutes. I've gotten to the point where I just don't stress - let it happen. They'll let you out with a couple minutes to spare and Air Canada will force you to run to your gate. Air Canada's agent said it's a common practice just to hold people up until the last possible second. People were getting super mad at the CBP agents, who would just yell back at them, and then other people were angry with the airline agents. No one can help, so just sit there and let them take their time.
 
My bags had already been pulled from the flight in both instances, but just as a heads up. Deep breaths.

You’ll be fine on the way there. This is just on your way back to the states that you will need a bit more time. (When you so pre-clearance in Toronto on the way back).

Oh they know what theyre doing there. You wont have a problem. 

Which airport are you flying out of on the way home?

It won't hurt, but there's nobody in immigration to show it to. Exiting the US has no immigration counters. The Canadian passport is sufficient to fly home for the airline staff to board you.

Just to add to the other replies. 
Depending which Canadian airport you are traveling through on your way back you will clear customs and immigration there before you board the flight to the US. If you will clear in an airport that you have a layover in, you might want to make sure you don’t have a quick layover.
My experience is based on Vancouver but I would give yourself extra time at the airport as each time I travelled with the combo card I had to go to the back room to process the AP which added 30-45 mins each time depending on how busy they were that day. But the extra time varies from person to person and airport to airport. (I was also traveling at non peak times on weekdays on purpose).

Also of note: if your name differs between that of your passport and AP, you need to carry evidence of the name change (i.e. a marriage certificate is a legal name change document).

You can fly with a Canadian passport. You won't need to present anything related to US immigration on the flight out.
When you return, you would use the Canadian passport as well. When you go through POE, present the passport + AP.
Note that POE can be in Canada...a couple airports abroad have preclearance, including a few in Canada (https://www.cbp.gov/border-security/ports-entry/operations/preclearance).