The popularity of Raptors 905 absolutely shows that Mississauga could support a larger indoor stadium. Something with ~10000 seats (like Budweiser Gardens in London, Place Bell in Laval, or Scotiabank Centre in Halifax) built with the ability to easily expand to 15000+ in the future would be perfect. There are plenty of other potential occupants through some of our fledgling fast-expanding leagues (NLL and CEBL), the ECHL, WNBA, etc, not to mention NBA-G and the OHL, in addition to being used for more concerts and events.
I'm pretty confident we will see public interest grow very quickly for a new arena downtown after the Hurontario LRT is online.