Regarding the Dieppe Raid;
"In April 1942 General Bernard Montgomery and Admiral Louis Mountbatten began to plan the invasion. It was originally due to take place in July but bad weather resulted in it being postponed until August."
(from spartacus.schoolnet.co.uk)
The British were in an impossible situation. The Americans were pressing for a second front landing in France, and, with the Russians were questioning the resolve of the British to fight. The surrender of Singapore, and then of Tobruk, to numerically inferior forces only heightened the suspicions of Britain's allies. A major raid was required, first to prove Britain's desire to fight, and second, to prove the techniques required for an invasion landing.
The British had three preliminary plans available to them, Operations, RANSACK, IMPERATOR, and RUTTER. Both RANSACK and IMPERATOR were corps sized operations requiring several days ashore. The British, however, had only enough landing craft to land a brigade. RANSACK was considered to be too large to be successful, and IMPERATOR, which included a penetration to Paris, as too risky. By default RUTTER was chosen.
Having approved the operation, command was given to South-East Command (SECO), GOC, General Montgomery. The original plan of flank landings over two tides was amended to a frontal assault during a single tide. Having decided on a general plan the time had come to choose the formations to take part in the assault. Canadian troops had arrived in Britain in 1940. They had been kept defending England from invasion since that time. Unlike the Australians, New Zealanders, or South Africans, Canadian soldiers had yet to see combat. Their general officers had been pressing for involvement in some operation if only to gain experience. This seemed to be the perfect opportunity for them. Based on results from recent exercises, the 2nd Canadian Division was chosen to provide the units for the assault.
The frontal assault had already been decided upon, as had the objectives of the raid. The Canadian staff only filled in the operational details. The original plan also called for an airborne assault on the batteries defending the Dieppe area, and a bombardment by heavy bombers to suppress fire from the beaches. In the later stages of planning the aerial bombardment was cancelled.
On the day the operation was to be launched the weather was unsuitable for parachute operations. The operation was first delayed, then cancelled as the weather did not improve. Disappointed by the cancellation and desperate for a raid, Montgomery's advice that the raid be cancelled for all time was ignored. There was insufficient time before the planned landings of Operation TORCH to train troops and launch a new operation. It was decided to relaunch RUTTER under the name of Operation JUBILEE. The same Canadian units that had trained for RUTTER would be used, but this time Commandos would be used instead of parachute troops.
Looks like Mongomery didn't have anything to do with the planning and it was like him to not want to launch an attack without everything being "perfect". But his name does come attached to the Dieppe Raid.