I'm intrigued that your suitcase would be opened if checked in. I would have expected that more as carry-on....
I fly Air Canada. And have not used an U.S. airline for over a decade.
All the airlines can and do open luggage, especially when the x-ray shows a jumble of metallic objects. I also put a note in with my Friday, and while I am pretty sure it's been opened from time to time, it's not been damaged. Touch wood.