On August 23rd, Nikon will officially announce their two full frame mirrorless cameras: Nikon Z6 and Nikon Z7. While Canon is not in a rush to enter the mirrorless market, as rumored before, Canon may not announce their full frame mirrorless cameras before Photokina 2018 in September (There still a chance Canon will announce their development announcement before Photokina). The official announcement will be after Photokina 2018, most likely in October, and the release date for the first Canon full frame mirrorless camera will be at the end of this year or early next year.
Currently, there are also two Canon full frame mirrorless cameras in testing, one is Canon EOS M style full frame mirrorless camera, and the other is Canon DSLR style full frame mirrorless camera.