The nights are cold in September, be prepared with a good sleeping bag.
You could encounter anything in term of météo, snowstorm one year to full hot sunny days the next.
Rifle? as big as you can handle well.
Get in the best shape you can, you'll enjoy your trip rather than suffer it!
Don't hesitate to send me a PM, especially if you'll be more comfortable in French. Funny, I'm going moose hunting with my cousins in Québec this coming September!