What is a GSP, why do I have to pick one?
Telco ISPs are required to “unbundle” their choice of Global Service Provider, the network used to carry your traffic out of the Telco ISP. Most ISPs do not show this separately. It seems that Bell ADSL is showing GSP as an item of choice, ie, you may select from a couple of choices of backbone. Your choice will probably make no difference, nor can you make it in an informed way.