Bears

There is an informative write up about bears on the Inside Banff : Safety page here at TripAdvisor.

Mosquitoes

Mosquitoes can be a nuisance in the Canadian Rockies in summer, and preventing mosquito bites is especially important because the mosquito-borne West Nile virus has infected a few people in Alberta in recent years.

It is wise to carry a spray bottle of mosquito repellant in the day pack that you should have with you for other reasons (to carry your jacket when it's not in use, to carry your water bottle, etc.).  If you've forgotten to bring mosquito repellant from home, it's readily available from the stores in the mountain resort towns.

The mosquitoes are worst in the evenings. In addition to using mosquito repellent, it's good to cover as much of your body as possible.  A  long-sleeved shirt, long pants / trousers and socks will do the trick,, although you may wish to spray your clothing with mosquito repellant for extra protection.

The temperature almost always cools off in the mountains in the evenings. It's normal for night time temperatures in the mountains to be in the 7°C (45°F) range. Sometimes the temperature drops to the freezing mark, even in the middle of summer.  So you usually need to add layers of clothing in the evening anyway.

Many properties in the Canadian Rockies do not have air conditioning. As you can probably tell from the temperatures that have been quoted, there would be little use for it.  All you need to do at night is open your window, and nature will condition the air for you quite promptly.

It is fairly common for hotel rooms in the mountains to have mesh screens on their windows.  When you are looking for accommodation, it would be a sensible precaution to ask if there is mesh screening on the windows. 

Giardia lamblia

This little beastie is a protozoan parasite that causes symptoms similar to Amoebic dysentery.  Because of the small but finite chance of contracting Giardia lamblia, never drink untreated water from lakes, rivers and streams.  Carry with you a bottle of commercial bottled water or a bottle that you have re-filled from your hotel tap.