There's no guarantee that you will be seated at a table with a good view of IllumiNations. La Hacienda has some tables with an excellent view, some with an okay view and some with no view at all. You can ask when you check in, but pretty much everyone wants a window table and not everyone can be accommodated. This is a restaurant where a number of posters have reported that they were not allowed to wait for a view table. Instead, La Hacienda frequently seats according to the next available table for your group size.
If seeing IllumiNations is important, plan on finishing dinner and finding a good spot around the lagoon.