Well to provide some background:
Britain had signalled its intentions to end appeasement when on March 31st 1939, Chamberlain had guaranteed aid to Poland. This was followed by a bill to introduce conscription being passed on April 27. Hitler tried to play the victim card by calling out London's "encirclement policy" in a speech to the Reichstag on April 28.
On May 23rd, in a meeting with Wehrmacht commanders and chiefs of staff, Hitler had declared his firm intention to invader Poland for 1) lebensraum and 2) to prevent it from joining an encircling alliance against Germany, having already approved "Case White" (plan for the invasion of Poland) on Apr. 3.
But before this could be put into action, the matter with the Soviets had to be settled. At first, Germany thought that Russia would side with the Western powers. In Spring of '39 Soviet foreign commissar Litvinov had made overtures to Britain and France to form an alliance to check German aggression, but he was rejected. When Litvinov was replaced by Molotov, the Germans took it as a sign that there was, according to the German ambassador to Moscow, "a guarantee that foreign policy will be conducted on the lines laid down by Stalin." On August 20, Hitler sent a telegram to Stalin declaring his intention to invade Poland. Russia would agree to an alliance, only if Germany agreed to the terms laid down in the special secret Protocol of the Molotov-Ribbentrop pact that dictated that conquered Poland and eastern Europe would be split into spheres of influence. Germany didn't dally on this, and signed the pact without hesitation as they had already set the date of the Poland invasion at August 26.
Soooo, getting back to the crux of the question - what did Hitler think of Britain and France when making these decisions? He saw their leaders as "mediocre vacillators." Britain was not going to be much aid to Poland as they were going to have their hands full in the far east with Japan, Italy was a check on both Britain and France in the Med. the Luftwaffe had a 3-1 manpower advantage over the RAF, they wouldn't be able to field more than 5 or 6 land divisions - Hitler summed it up by saying "it seems to me impossible that any responsible British statesman dare, under these conditions, accept the risks of open warfare."
As for France, Hitler looked down on both their armaments and manpower and argued that neither Paris nor London would invade through neutral territory. he believed the worst that would happen is that Britain and France would recall their ambassadors and maybe blockade Germany.
Unfortunately, France and Britain didn't see it that way. France reaffirmed their commitment to help Poland, thinking that the combined air forces of France and Britain could carry out bombing raids on Germany. On Aug 25th, England and Poland signed a Mutual Assistance Pact. Hitler was surprised and called off the Aug 26 invasion. He met with the British Ambassador and laid out his case for Danzig and even tried to sweeten the deal by offering Wehrmacht assistance to Britain if needed if they would consent to stay out of the Poland situation. Britain rejected the offer. Hitler plowed on ahead, setting a September 1 deadline. Last minute negotiations between Britain, Poland and Germany were brushed aside. At this point it was too late and the gears were already in motion.
And that's a way too long answer for this, but it gave me a chance to break out Vol 1 of my WW2 encyclopedia.
