Oakville Humane Society is a "no-kill" facility but will put cats brought in up for adoption after about a week once they pass the health check.
I would recommend contacting Paula ASAP and filling out a lost pet report also. After that you can review the adoption page to ensure your cat doesn't slip through into the adoptions area.
Paula@oakvillehumane.ca (Lost and Found co-ordinator)
http://www.oakvillehumane.ca/adoptions/online.html
Good luck with your search!