You need to get the files from the PowerTap into .fit format, then you will be able to upload them into Intervals.icu. I think Golden Cheetah might be able to do that conversion:
Golden Cheetah exports all regular fields in the FIT file but not the developper fields like HRV. Found that out when I was trying to crop a part for better analysis of dfa-a1. All HRV data was stripped.