Complex sentence: It was planned that Black Prince would be a Commonwealth project, however since the government of John Diefenbaker in Canada was already spending more money than publicly acknowledged on Alouette and Australia was not interested in the project, these two countries were unwilling to contribute.
Split into simpler sentences: It was planned that Black Prince would be a Commonwealth project. However, since the government of John Diefenbaker in Canada was already spending more money than publicly acknowledged on Alouette and Australia was not interested in the project, these two countries were unwilling to contribute.