I only hike outside National Parks, usually in wilderness areas, because I have two shetland sheep dogs along.
Before the shelties, bears were a problem for me as a solo long distance hiker for years, and I had some memorable, but not pleasant experiences. Since the shelties, not a bear to be seen for over ten years.
I understand why you want to see the parks, and would suggest a small music player loaded with whatever you find the least annoying and well within the grizzly auditory range. If they hear you coming, they will usually take off; but not always, so keep an eye out.