If it's the same information, it's automatic.
If they want to change addresses in Canada.... Let's say they move back to Canada for two years. An election is every four years in this country. They may move back, and then they may move back to Washington, D.C., if they get another job offer. They will have changed addresses in Canada, but the system won't have had time to catch up with it. Then they are caught in the process of...if they updated the list while they were in Canada, their address on the register of electors, and that matches, therefore, they're registered.
It starts over again. It satisfies the requirement to register again and makes it easy. It's not as easy as if you're in Canada. That is an important nuance, but it's one I've come to accept as being essential.