Booking a Lake Side View at the Sequoia Lodge does not necessarily guarantee a view of the castle as the "lake" runs around each side of the hotel so you could be facing the Newport Bay Club or the New York. However if you request a particular type of room before you visit, the hotels will often do their best to meet your requests. We have just returned from the Newport Bay Club hotel and I had requested a top floor room as my autistic son likes to over the lake and Disney Village. The receptionist was extremely helpful and found us a room on the top floor with a balcony and an excellent view of the castle.
With the Newport Bay Club there is an extra charge for Admirals Floor Lakeside View rooms which covers floors 5 - 8 but it was worth every penny to see the excitement on our sons face when he saw the firework display.
If you can though, I would recommend watching the firework display at the park at least once to see the lighting effects on the castle . Watch from near the castle rather than the bottom of Main Street to get the best view.
Enjoy your trip.