You will get to pick from the Midsize SUV aisle. It will have Equinoxes (Equinoxi?) and possibly other similar sized SUV's. I haven't rented from that emerald reserve aisle recently, so I'm not sure what else might be there. There may be nothing other than the Equinox.
Emerald Aisle is where you usually find more variety. For example, if there are no more parking spaces in the midsize SUV Emerald Reserve aisle, they may park midsize SUVs in the Emerald Aisle. Then people who reserved an intermediate in the Emerald Aisle can take that SUV and still pay the intermediate price. Generally, if you rent Emerald Reserve, you get that kind of vehicle, I've never personally had a situation where there's an "upgrade" in an Emerald Reserve spot and I rent quite frequently.