There are plenty of E+ seats available..no worries there. I checked. And you also will have no problem using E+ access and earning miles in your Aeroplan account. Just call reservations after booking the ticket and they can set it up for you.. there are actually 2 mileage number fields, 1 for mileage earning, and another for things like E+ access. I would definitely buy the E+ access. Just so you know... there are only 2 differences between E+ and regular economy... both make it worthwhile to me.. 1. a few inches more legroom (the seat is identical to regular economy seats, just a little more space in front of you), and 2. You get to sit in the front part of the economy cabin which means you get off the plane quicker and can get further ahead in the immigration line (and you do get served your food and drinks quicker since the FA's start serving in the front). No other differences..no free booze or better food.

The E+ seatmap for flight 928 ORD-LHR on 10/3 has several E+ seats available but very strangely all the seats on the right hand side of the plane in E+ show taken as well as the middle and right aisle seats of the center section (767). Someone else take a look... very odd.