I don’t know about the Giant, but on my Kestrel, I put the cadence sensor under the seat tube water bottle cage. This is just about the closest possible spot to either my wrist or the handle bar mount and the cage and bottle keep me from brushing against it and moving it.
I attached mine to the chainstay. I had to open it up and move the jumper to increase the sensor range (tradeoff is shorter battery life). Works great! I did the same thing to put the speed sensor on the seat stay. i think the directions for moving the jumper were on the polar Australia message board.