Took the family out to Glacier last summer (August timeframe). In a word, "spectacular". Didn't fish, but hiked a ton (over 700 miles of hiking trails, so something for everyone). For hiking trails, our favorites were Grinnel Glacier and Iceberg Lake. Both on the eastern side of the park, so a little less traveled, and I think a better chance of spotting widelife. We saw a mother Grizz with a cub (fortunately at a distance) and a couple black bears. On the Grinnel Glacier hike the two groups of hikers in front of us stopped at one point, and when we caught up to them, the front group said they had spotted a mountain lion not far off the trail. As they say, usually by the time you spot a mountain line, its already too late, but the three groups together made up six people, so probably not something he wanted to deal with. Also did Hidden Lake overlook hike which was beautiful (we hiked all the way down to the lake, the return being a bit of a lung buster), easily accessible from Logan Pass. One of the Big Horned Rams came within about 10 feet of my oldest daughter. In hindsight probably not the safest thing in the world, but quite the experience. Only hike we didn't do that we wanted to was Highline Trail, but didn't have enough days to get that one in.
As stated, didn't fish, but did some white-water rafting. Unfortunately it was August and it had been a dry summer, so water levels were way down. Still enjoyed it but the class 4s and 3s were only 3s and 2s, so not quite as exhilirating. Definitely want to do the Going to the Sun road, absolutely breathtaking, and a bit of white knuckler if you are driving. I believe it is the only road that you can take that spans the complete park from east to west, so it is hard to avoid it. If you have folks who are afraid of heights (like my wife), make sure the sit on the "inside" half of the car. Elevation change is something like 5,000 feet over the course of 5 - 6 miles, so it will get your attention.
We stayed at a Airbnb in Whitefish (about 15 miles from the Western Entrance to the park). Beautiful little town with all kinds of boutique shopping and restaurants. You can tell there is a lot of money there. Also home to Whitefish Ski Reort, which has a really good reputation. They have zip-lining in the summer months (although we didn't have time to do that). Plenty of nice areas with amenities on the west side of the park (Whitefish and Kalispell), the east side is definitely more rural. Also if you are willing to drive an hour or so south of Kalispell, there is Flathead Lake. Gotta believe there is a lot of good fishing there. Supposedly the 5th largest lake in Montana and absolutely georgeous.
Highly, highly recommend the trip!