First of all, the merchants are supportive of a harmonized tax. The challenge with internalizing the tax is that the tax is not the same right across the country. There is one province specifically that has no provincial sales tax, so this makes it very difficult for national retailers wanting to advertise a single price because in fact they could not if you force the combined tax to be hidden in the price of the goods.
On November 2nd, 2009. See this statement in context.