I ABSOLUTELY LOVE my GMC Acadia. It is very roomy and the standard setup is to have 2 seats in the 2nd row with space in the middle for your older daughter to access the 3rd seat.
BUT, I have to say that my last vehicle was a full-size truck, so I can't really say how the Acadia compares to driving a car. I know my friends have driven it when we share driving on trips, and they like it. I just know I would MUCH rather drive it than a minivan.
Another possibility, since the Acadia is pretty roomy going across, is to get the 8-passenger like we have, and you could put the baby in the middle and your other two on either side. The 8 year old could probably unbuckle the baby while you help the 3 1/2 year old out of the car, then you could grab the baby. Seriously, the back seat is very roomy; I ride next to our son in the back on long car trips. 5 adults in the first two rows is do-able. I usually keep the 3rd row folded down for trips to Sam's and just other gear we haul around.
Standard is 7-passenger; optional is 8-passenger. We only have one child and that is how things will stay; but I bought this car after that decision was made, have had it for 2 1/2 years, and still wouldn't want anything different. Love it.
Happy car shopping!