Reddit reviews Handbook of the Canadian Rockies

https://www.amazon.com/Handbook-Canadian-Rockies-Ben-Gadd/dp/0969263112 A monster of a book, but it's an amazing resource. At the end of June, you will still run into snow at higher elevations, like passes. I'm not sure how backcounty you are planning on going, but unbridged rivers can also be a major issue at this point in the season. Lots of melting snow means fast, cold, deep, murky water.
When it comes to booking backcountry sites, the good ones tend to book up quickly. They key is to look for the "undesirable" ones. These are the ones that are not on a well-known loop and are a LONG day's hike to get to. For example, Flint's Park. If you go even further, random camping is permitted.
Buy bear spray, know how to use it. Learn how to look for signs of bears. Digs, poop, prints, etc. Announce your presence, especially one moving from one area to another. Crossing water, moving from forest to meadow or vice versa. Cook and store food/smelly things in an area separate from where you camp.

My favorite is https://www.amazon.ca/Handbook-Canadian-Rockies-Ben-Gadd/dp/0969263112

It has very detailed writing of the geological history, ecology and zoology of the Canadian rockies.

Get yourself a copy of this:

Handbook of the Canadian Rockies

Though this one does cover a lot more than just the geology..