If you get through the course and are offered a place with Easyjet then you'll be given a chance to state a preferred basing. Whether or not you'll get the base of your choice is up to the compnay but there generally isn't a problem with getting where you want within a fairly short timescale (a few months). Most people go on the base transfer list and get what they want before they finish type rating.
However, you have to realise that it is by no means sure that you'll get EZY. Depending on the time of year you may be much more likely to go to one of the other airline partners (the charter operators tend to pick people up around Christmas time). You do have a right of refusal but i'm not aware of anyone ever using it in the past. With minimum hours and an aviation industry so prone to volatility imho it would be silly to turn down any offer, especially when the t&c at all the partner airlines are so similar.