I had the room with balcony (3rd floor) at Danieli last year, but the balcony was not wide enough to enjoy the drink. We could just stand and watch the people walking in front and lagoon with islands.

Westin is located in canal front, and as other said you could see Gondolas/boats and grand canal.
If the terrace/balcony is wide enough to put chairs and a table, you will have the great time to enjoy the magical Venice.