I live in Canada and plan to drive to Yellowstone and Mt. Rushmore this summer. How much time should I plan on spending? Should I make reservations for accommodation in advance? What other areas can I visit along the route? All suggestions would be appreciated. Thanks.

Our family has traveled in South Dakota several times and never get tired of it. If you plan on traveling the first full weekend of June or early in August, I would suggest that you get reservations well in advance. Between Yellowstone and Mt. Rushmore, there is the Devil's Tower in NE corner of Wyoming that is awesome to go see. Mt. Rushmore deserves at least a full day because your trip is not complete without going to the nightly lighting ceremony. If you plan on going any further east in SD, there is the Badlands about 60 miles from Rushmore and Wall Drug(don't worry,you can't miss Wall Drug). Some of the attractions around Rushmore include: Crazy Horse Memorial(an annual Volksmarch up to the face is the first weekend in June), the 1880's Train, the pigtail bridges, Custer State Park, and the Mammoth Site(in the area) are all things that we have enjoyed in the past. As you can see, there is plenty to do. But watch for the weather, it snowed last year the first weekend in June.

For those two places, I would plan no less than two weeks to enjoy the full amount of fun in those general areas. Yellowstone and the Tetons (do NOT miss the latter) deserve a little less than a week, then a few days to go from Yellowstone to the Black Hills (Devil's Tower is a must-see, as is the Buffalo Bill Western Historical Museum in Cody), and then a little less than a week in the Black Hills Region. There, don't overlook Badlands Nat Park, Crazy Horse Monument, Custer State Park, Spearfish Canyon, and the Homestake Gold Mine Tour. Depending on your interests, you may wish to visit several of the other touristy sites and/or go hiking in the Hills.

If you are going in July/August, you MUST have reservations at Yellowstone, preferably way in advance. The Black Hills will have some spots but you may not get what you want. As always, the earlier in the year you go, the better your choice of places to stay will be.

With regard to your trip, I urge you to get in contact with Amfac, the Yellowstone concessioner, immediately because cabins and lodge rooms are already heavily sold. My son plans to be there in June and he could not find 4 nights at any one place; he had to split it up. I will be there in August and rooms at the Old Faithful Snow Lodge cabins are all gone for my time frame.
There are decent motels in West Yellowstone, but that is 30 miles or so from the geyser basins. But you may need to see refuge there.
In the Tetons, Jackson townsite is not all that far off. But, you might try Signal Mountain Lodge. It is good, but a little expensive. The location cannot be beat.
In my opinion, and it is strictly mine, I would give preference to Yellowstone over that defaced mountain called Rushmore. Sorry, and I catch a lot of flack over this view, but to me someone took a jackhammer and defaced a perfectly good mountain. We already have jillions of stone likenesses of those men, so why tear up a good mountain for more of the same? But that is my view.
I will be happy to discourse at length my "take" on Yellowstone. You gotta see Castle Geyser and Grand Geyser do their things. They are spectacular. And yuo can check in at the visitor center to see when the predicted eruption times are. Grand takes some geyser sitting to see, but believe me it is worth it.
Take your lunch or supper as the case may be and chat with the other geyser fans. Castle is fairly predictable within an hour window of time.
And the hike to Lone Star Geyser through the beautiful, unburned area of the upper Firehole River is scenic and tranquil. The trail is obvious and relatively flat with no serious obstacles.
The geyser is no slouch either; but it is not traced officially on predicted times. Take your lunch and have a seat in the trees and enjoy life.

Do not vacation in the Black Hills area at the same time as the national bikers rally in Sturgis -- I believe it is the last week in July. You might check that out. During the rally, it is almost impossible to get accommodations and difficult to get around. Be in the Black Hills area before or after the bikers rally for a little more peace of mind.