I lucked out the first time I went as I ran into a guy the day before my visit to the park that created maps of day hikes in Glacier National Park - Jake Bramante. I highly recommend Jake's Glacier map as he does a great job of outlining day hikes, allowing you to decide what you want to do. https://hike734.com/hiking/
You can see that Jake ranks his favorite hikes on this link, which is very helpful.
My all time favorite hike is the about a half mile of the trail right across from the parking lot to Logan's Pass - It's the first mile of Highline Trail. Logan's Pass is a must, but many miss the beginning of "Highline Trail", which is right across the street from Logan's Pass parking lot and is a MUST.
Also, Many Glacier (the North entrance on the East side of the park) is where I saw Moose and a bear (from across a field, fortunately).
GNP is a great park. Enjoy your trip!