I was present in Quebec City in 2008 when we were celebrating 400 years of the history of Quebec. A very concrete suggestion that seemed to work extremely well was that the city, I think with federal and provincial funding, provided project funding, and people could apply for projects. One I was involved with was a very innovative, digitally based exhibit on the history of the local Jewish community. It was creative in the sense that it allowed the community to work together. It built community vitality while creating its own history and communicating it online.
Projects ranged from that to planting a certain number of trees. I think the argument was something about the historical territory or something like that. They were absolutely swamped, apparently, with projects and had a hard time choosing among them, so I don't think the ideas are lacking.
To answer your question, you could provide a framework defining what is being celebrated and describing the opportunities for developing projects. It could be projects devised to have a certain content, whether linguistic duality or the history of the minority language communities or the history of Confederation as an act, or something like that. Then the ideas will come.