We got married last summer at the Rimrock Hotel in Banff and loved it. We had some similar criteria - wanted an outdoor ceremony with a nice view and we had 100 people. In the end we were between the Rimrock and Silvertip in Canmore but there were a number of reasons we went with the Rimrock.
Silvertip books years in advance so they weren't able to offer us any Saturday dates even though we were booking a year out. Also, they were nickel and diming on every little thing like charging us per chair to set up for the ceremony. Also, the fact that there wasn't a hotel for our guests there was a huge factor.
The one downfall of the Rimrock in your case is that they won't let you bring your own food or drink in but the food there was amazing. Our budget was initially 25k which ended up being more in the end (due to decorations, flowers, dress alterations etc.). Be warned that things add up quickly and there are a lot of costs that people don't think about for weddings! 20k for the amount of people you are planning on having will be tight - a decent photographer will take up 15-20% of that budget off the bat. That being said, if you're not picky about decorating the space, spending money on flowers or anything and just keeping it simple then it's probably possible! We saved a lot of money by doing a lot of the decorations ourselves and I'm still planning on getting some money back by selling what's left on kijiji. (Side note - anyone getting married, I have a lot of white and grey wedding decorations to sell if you're interested, haha).
If I had to do it over, I would probably get on a plane with my close family and friends and just get married on a beach in Hawaii...less stress, less cost, and you're still married in the end!
Just my two cents! Highly recommend at least checking the Rimrock out though
