We had the same issue from when we landed until we fond a job/which allowed us to secure an appartement.
We have done short term renting for 3 months and unfortunately you have not much options. Also, if like us you have a pet, most short term accommodations will be overpriced on Airbnb.
We managed to save a bit of money by checking:
- Sublets on Craigslist/Kijiji (be aware there are a lot of scammers there, don't pay anything in advance until you visit the place and sign a sublet agreement)
- Use Padmapper/Viewit.ca or other websites. In the "minimum lease requires" box, some landlords don't indicate anything. I've contacted a few and surprisingly, some were OK to rent month by month
- Hotels - some might actually be cheaper than renting for 4 weeks on Airbnb
Good luck