In the Global vision north of 70°, you simply switch from magnetic to true and make sure you have any of your screens with maps on "map" instead of "plan" mode since it is required per the AFM (I haven't tried to put it into "plan" mode over 70° to see what happens). You are also restricted from using the heading synch function while in True mode. You will have CPDLC over Alaska, Canada, and Greenland (I haven't tried it anywhere else above 70°). There are patches of HF and areas of VHF up north. Overall, it isn't much different than regular oceanic crossings.