The monzas will fit no problem.
The mk5 stud pattern is 5x112 for future reference.
What size wheels are on the car now??
If you have a early GT TDI the standard wheels were 16's so the tyres wont fit.
If you have a facelift GT TDI then the standard wheels were 17" so you could use the tyres on the 17" monzas.
If you have a TDI then you could have 15" wheels