For most jaw-dropping views from a restaurant in Banff, you can not do better than the Sky Bistro at the top of Banff Gondola. Sitting at 2415 meters, the restaurant operates on a "farm to summit" premise and, when available, sources as many local ingredients as possible. If you book one of their dining experiences, it's a pretty good deal if you had plans to head up the Banff Gondola anyway.
They also offer two unique combo tickets that include the price of the Banff Gondola, one a daytime Banff lunch for around $105 and the other their dinner option for around $144. Keep in mind they do use dynamic pricing based on demand, so it's possible you find different price points. However, you can always order a la carte if you want to book your gondola ticket separately. Reservations are only available 30 days in advance, but walk-ins are welcome based on availability.
We've only dined here once, and it was a special experience. Sky Bistro is one of the most scenic restaurants in Banff, and we've climbed to the top of Sulphur Mountain many times and can attest to the view.