Actually, I don't think walking for an hour is going to hurt anyone's strength. Lots of powerlifters do this. IMO that would be a better option than a killer HIIT or Prowler session as these are much more demanding and could affect the quality of future strength training sessions as well as recovery. Moderate interval/prowler type training would also likely be a good idea. The point is that cardio shouldn't be very taxing if you're goal is strength.
Of course, the best way to lose weight is with diet modifications.