Two different beasts. A consortium would a be a collective group that has established connections and puts together benefits and passes them on to their members. They offer training and other tools to help agencies. I do not believe that you can be an individual agent to be a member of a consortium unless you are your own agency (own accreditation, probably certain volume as well).
A franchise is a company that has an established business plan and marketing strategy that you "buy into" at usually a hefty price but they supply you with everything you need to run your business but you MUST follow their business structure and strategy. Like Macdonalds is a franchise... you use their name and branding and systems but its your own business. But you can't make the burgers they way YOU like...you must use their recipe.