I found this on an Amazon search. I searched because I have a smallish book that must be close to 20 years old, that I was going to offer you, but this is from 2002, so you'd probably rather have it.
As noted above, it's mostly lake fishing in the park. A lot of the smaller lakes are at or above treeline though, so it's not essential to have a float tube because you can work many of them fairly well from the bank or shallow wading.
"Fishing Glacier National Park, 2nd [Paperback]"