Sure. The AC lines are excellent for short distances of up to perhaps 1,000 miles. If you get anything beyond that, you have to deal with stability issues.
With DC transmission, you can go a very long way. One of the longest lines we have in North America goes from Los Angeles to Oregon, and it's a DC line. The advantage of DC is that the systems can essentially run isolated. Quebec, for example, is completely isolated from the rest of the North American grid, because they connect—through New Brunswick in some cases, through Ontario in others, and directly in others—only with DC transmission.
DC transmission lines are expensive because of the converter stations. You have to put a converter station at each end, and you also have to have an AC source available at the end to help that converter station work. They are a bit more complicated, but in fact, if you are going to start tying the Canadian provinces together, you are going to find that the U.S. is divided into two.