I'm not sure he had "good reasons." He certainly had reasons--namely that since Britain and France had been unwilling to go to war over Czechoslovakia, they must be bluffing about their willingness to go to war over Poland.
So I believe that Hitler firmly thought that the British and French governments' response to the invasion of Poland would be to break off diplomatic relations, broadcast propaganda, step up weapons procurement, and then calm down. Once they had calmed down--or so Hitler thought--his ambassadors in the west could calmly talk to small groups about the magnitude of the Communist menace. Operation Barbarossa could then have been launched with trade links from Germany to France and the British Empire intact. And then throughout Eastern Europe Communist Party members, Jews, and Gypsies would have been shot on sight, and Slavs either enserfed or worked to death.
And--or so I think Hitler thought--the British and French governments would then wring their hands about the massive slaughter in Eastern Europe, but take no action.
The problem, however, with this line of thought on the part of Hitler is the problem with game theory in general: the assumption of excessive rationality on the part of the other strategists, and the assumption that your view of the situation is their view of the situation as well. Certainly it made no sense in terms of game-theoretic rationality for Daladier and Chamberlain to stand aside at the German conquest of Czechoslovakia and declare war over Poland. But in 1938 a politically-powerful slice in the West saw Hitler's aims as limited to the ingathering of the German ethno-nation--not something worth fighting a world war about. And by mid 1939 that slice of opinion was gone...
So when the chips were down Chamberlain and Daladier did declare war, and Roosevelt tried as hard as he could to shift congressional opinion by putting U.S. destroyers in positions where German submarines would torpedo them...
Brad DeLong