What determines whether or not an addition reaction will proceed through a carbocation or bridged-ion intermediate?

enter image description here

I'm unsure about how I would deal with this addition reaction as it isn't like the typical ones I've learned. I'm pretty sure THF would be an inert solvent so would have no effect on the reaction. My main concern is how PhSBr would react with the double bond? When drawing the mechanism out what kind of intermediate would I go through? As a general rule how do I decide what kind of intermediate to choose. I know that it if it is HX or X2 what to do, but am unsure it it is something like what I have above.