Canadian oil and gas trusts are in the midst of positioning themselves for a federal tax change effective next year in which trusts essentially will be taxed the same way that corporations are taxed.An Oct. 31, 2006, proposal from Ottawa has been dubbed the great Halloween massacre by some in Calgary, headquarters for several of Canada's largest trusts. Existing trusts received a 4-year grace period from the tax change so their effective date is Jan. 1, 2011.Traditionally, trusts paid little or no corporate tax, enabling them to distribute most earnings to their investors or unitholders. The 2006-07 legislation and resulting tax law applies to all Canadian income trusts, of which energy t...