The Japanese had two parallel but unequal programs, the Ni-go operation, sponsored by the Army and its poor relative, the Navy’s F-go program. Neither was very far along, though there are exaggerated claims made, from time to time, about how close it all was.
Neither the British nor the Canadians had a realistic chance of producing a weapon, working against severe constraints on manpower, brain power and funding/resources. Both did, in concert, do a great deal of early theoretical work, under the MAUD committee, and the Tube Alloys project.
When the US and the Brits/Canadians began working together, the industrial capability of the US, as well as the theoretical (name removed by moderator)uts from all 3 countries, led to the success of the Manhattan Project. But while both Britain and Canada had brains and Canada raw matelrial, neither could have produced a bomb during the period the war lasted, or might have lasted.
The most serious early leaks, though by no means the only ones, came from Klaus Fuchs, a German refugee and Tube Alloys man, who started leaking even before he reached the US, and Allan Nunn May, a British scientist with impeccable Communist connections and sympathies. His perfidy was revealed when Igor Gouzenko defected in Canada. Lots of other good stuff came out of that escape.