Well first off, congrats on the engagement and welcome to the Wedding Wire community!!
As for weather - I'm getting married October 5th and my worry over weather is extremely present! I would say that worse comes to worst we buy a whole bunch of umbrellas for everybody or see about renting a tent but that wouldn't be until about 2 weeks before the wedding when the weather predictions are more reliable.
If it snows I wouldn't complain either
If you want to avoid the worries all together I think that an indoor venue is fine - here's a link to some in Saskatoon that are listed on WW: Wedding Venues Saskatoon