LunarMist, it has been a long time since I contributed to Storage Forum, but your enquiry is something I know about.
I drive from Los Angeles to Cranbrook, B. C., just north of the western corner of Montana, once or twice a year. I leave in the morning and arrive at Cranbrook early evening of the second day, with one overnight stop. As you have been told, you need a Passport and proof of residency (Driver's License) to enter Canada. I also carry a "Canada Non-Resident Inter-Province Motor Vehicle Liability Insurance Card" which my auto insurance company provides me each year. This can be handy if you have the misfortune to be involved in an auto accident. I once was.
You can bring citrus into Canada but no fruits or vegetables that grow there. They allow at most one 750ml bottle of alcoholic beverage for your own use. You will discover that food, lodging, alcohol and gas are more expensive there, and since the Canadian dollar is now worth a little more than the US dollar, you are at a further disadvantage.
You mentioned that you may fly to Montana and drive to Canada. I strongly recommend this. Western Montana, accessible from Billings, provides easy access to the jewel of North america --- the Canadian Rocky Mountain Park System. The mountain scenery you encounter there is the most beautiful of all that I have seen in North America and Europe.
The parks have a short snow-free season: June, July and August. In the parks, summer daytime temperatures are warm to cool and some nights are cold.
There are four magnificent adjoining parks: Kootenay, Banff, Jasper and Yoho. You can easily visit all four by taking a circle tour in your vehicle. For example, drive north from Missoula along the Rocky Mountain trench, through Kalispell into Canada. Continue on Hwy 95 (an extension of US 95) along the trench until you enter Kootenay National Park at Radium Hot Springs. Stop there and enjoy the hot and cool pools and look for mountain sheep and goats on the cliffs above you.
In Kootenay Park stop to explore when you see signs identifying points of interest, then cross the Continental DIvide and enter Banff National Park. Do not drive to the town of Banff until you return to the U.S. Instead, head north on the Trans-Canada Highway 1A to Lake Louise. This is my concept of the world's most beautiful site. Take time to hike up to Lake Agnes and stop at the Tea House for refreshment. You can also rent a horse to make the trip. Continue to the five glaciers if you wish. Before returning to the Trans-Canada Highway, take a short side trip to Moraine Lake and the Valley of Ten Peaks. Rent a canoe and explore the whole lake. The mood of this lake is much different from that of Lake Louise, but it is also a beautiful lake. It has accomodations and a good restaurant.
After Lake Louise continue on the Trans-Canada Hwy until you re-enter British Columbia at Yoho National Park. A few miles into the park take a 10-mile side trip north of the main Hwy to Takkakaw Falls. It is not quite as high as Yosemite Falls, but a torrent of water flows all year round. You can hike a further 10 miles to visit Twin Falls and the most remote of all National Park Lodges. Continue a few more miles along the Trans-Canada Hwy, past the CNR Spiral Tunnels to Emerald Lake, another beautiful lake and Lodge.
A few years ago, friends and I were fortunate to get on the bus that took us to the Federally protected area of Lake O'Hara and its log cabin accomodations (perfect for a honeymoon). We made reservations for a late lunch at the up-scale Dining Room and continued on a hike around the lake and up the slopes, past three small lakes, to Lake Oessa at the foot of the glacier. I will never forget that hike. We barely got back in time for lunch. Lake O'Hara is on the B.C. side of the Rockies behind Lake Louise.
You can now return to Alberta and head to Banff and your return trip to Montana. But if you have the time, continue north to Jasper.
The 200 mile trip from Banff to Jasper is the most neck-wrenching sight-seeing trip you will ever take. The first must-do side trip is a short hike to the viewpoint for Peyto Lake. Continue north and stop at the Columbia Ice Field (largest water-shed in North America) where you can take a snow-vehicle trip on the Athabaska Glacier. Further on there are spectacular water-falls to visit. A side-trip to Mount Edith Cavel is rewarding. After a fresh rain you can watch snow tumbling off the mountain. Continue through the town of Jasper to Miette Hot Springs and enjoy the pool.
From Miette take a side-trip south past Medicine Lake to Maligne Lake. At the head of this lake purchase a ticket for the boat that will take you 10 mile further south to the viewpoint for Spirit Isle. This is one of the the most photographed sites in North America. Its scenic composition is comparable to that of Lake Louise.
You can now return to Lake Louise and on to Banff. This is a crowded little town in summer with excellent accomodations, shopping and restaurants. It has a lower level and upper level hot spring with fine facilities. I used to enjoy swimming in the pool at the Banff Springs Hotel. This is a grand hotel to visit, as is the Lake Louise Chateau. There are many side trips to take near Banff.
There are two routes through Alberta that will take you back to Montana. The fastest is through Calgary, then south to Lethbridge and the border. A more scenic route is the one that hugs the east foothills of the Rockies. It also takes you to the Waterton-Glacier International Peace Parks. These parks are worth a visit but they do not have the grandeur of the parks further north.
Most tourists visit Vancouver and Victoria when they visit British Columbia. I will head to the Rockies as my first choice.
Hope this helps, Joe