October's three-week strike by the Canadian Auto Workers union against General Motors Corp. will slice $700 million from GM's fourth-quarter profits, GM officials tell analysts. Then increased benefits pledged to United Auto Workers union employees will require a separate $170 million charge in the final quarter. Meanwhile, Michael J. Burns takes the helm at Delco Electronics, succeeding Gary W. Dickinson who is retiring. Insiders say GM is seriously considering combining Delco, which now is a part of GM Hughes Electronics, with Delphi Automotive Systems, developing the two into a new publicly traded company. At the same time GM warns Wall Street that Hughes, which is being positioned for sale, will face tough sledding in 1997 from continuing consolidation in the defense and aerospace industries.