CTV & Rogers have confirmed they will each hold a debate with only the Progressive Conservatives, Liberals, and New Democrats participating. The parties excluded will be the People's Alliance and the Green Party. Neither gave reasons for excluding the latter two parties (although I will present my own theory below). It is not like five people on stage is unmanageable. Federally, we have been having debates between 4-5 participants for years without difficulty.
Radio Canada is also excluding the People's Alliance and Green Party from the French debate. Unlike CTV & Rogers they at least gave a rationale for excluding these parties: they felt neither of the leaders were fluent enough in French.
The Reasons Why
Summary: Premier Alward, you are a coward. Although, to be fair, the Liberals and NDP don't seem to be in any hurry to ensure the people are presented with all their options either.