Hi, Sandiga, and welcome to RTA! You expressed some very valid things about the need to reserve in advance. If you are planning to travel, and have questions, please feel free to start your own thread. The one you responded to is over 5 years old now.
I will tell you, though, that the Waterton Lakes National Park is small in comparison to the US side, Glacier National Park. Waterton is easily seen in a day or so (unless you plan to take the boat trip or do some hiking). Not so with Glacier, especially needing tickets this year to drive the main drag, Going to the Sun Highway. I also agree that Jackson WY is super expensive in the height of either the summer or the ski season -- when you see that Motel 6 has rates over $230/night, you know it's high! We found accommodations in West Yellowstone, but after leaving Grand Teton, we drove around to the "backside" of the Tetons to stay.
Donna