There're no E+ seating on AC planes. If you have a tight connection perhaps you can request seating further up front. Where are you flying from to YYZ?

UA gold will be *G and you'll be able to use the YYZ maple leaf lounge if you're connecting. You'll get priority boarding with the Super elite, Elite 75/50/25k and *G.

You may be offered a LMU (last minute upgrade) when you do OLCI on AC.com (if you have an AC booking reference code). You can also ask to pay for upgrade at the gate. If you're flying on Y fare maybe you can use your UA miles to do an upgrade but it'll have to be requested with the UA MP program.

If you book your flight via UA.com they may offer a Y-up to buy up to J.