As far as I am aware there is no sound cancelling upgrade in the UK, I found the GLC to be very quiet. My advice would be to decide which model you would buy and ask for an extended test drive. Here are comparisons between the GLC and Q5, GLC is quieter:
https://www.carleasingmadesimple.com/data/mercedes-benz/glc/noise-level/
https://www.carleasingmadesimple.com/data/audi/q5/noise-level/
https://www.carleasingmadesimple.com/data/mercedes-benz/glc/noise-level/
https://www.carleasingmadesimple.com/data/audi/q5/noise-level/