Banff, AB, Canada < change city >

Response from the couple:
The gazebo is quite large, and was able to fit everyone on our guest list with room to spare, so rain wouldn't have been much more of a problem than anywhere else where you'd have to be exposed between your vehicle and the venue. Renting the gazebo doesn't include any fallback options, so you are at the mercy of the weather, I suppose. I've never seen bad weather in Banff, though, so maybe it's not a big issue. There are indoor venues in Banff, but we didn't use any of them, so I don't know about them.

http://www.banff.ca/locals-residents/recreation/facilities/central-park.htm