A Franchise is when you buy in to an existing company. An example of this is McDonalds, you can buy in to their business and basically open your own McDonalds.
Buying in to a franchise has advantages like, Existing and well known company. And also you will have limated liability, this means if you lose money you will only lose what you put in.
Where as a sole trader has unlimated liability, so you will have to find the funds your self if you lose money.
Also with a franchise the company you have bought in to will provide money where as sole trader as you are alone you will be expected to find the funds your self.
However the disadvantage of a Franchise is you will not have the final decision, the franchiser will have the last word. This is an advantage for a sole trader as all decisions are all yours to make.