You get to keep only enough to maintain a very modest lifestyle in a low-cost-of-living area, the rest of it has to go towards improving the world in some way.
Edit: Given the previous rules that you must maintain a very modest lifestyle in a low-cost-of-living area, would you rather choose to opt out and not have the money at all?
Invest the money, and use the after-inflation income to do the work.
That way, you have a constant and near-permanent resource stream with which to do the work. It’s only if the markets crash as a whole that you need to worry, and nothing says you cannot build additional revenue streams along side that wealth.
I would start with the most pressing issues for Canada - housing, and the homeless crisis that arises from shitty wages combined with exploding costs. Buy large tracts of land within each city, then economically force the cities to approve large arcologies that blend residential with business spaces. Make it super-attractive for even the wealthy to want to rent homes there, but turn around and then make assisted living units available in those same areas to low-income families and homeless people who want to get off the street. Have those communities to be tightly integrated across all social strata, so everyone benefits. Plus, actual social support that helps those traumatized by homelessness to get their lives together and return to being contributing members of society.
Exactly what I would do. Build tiny house communities for low income housing that sustain themselves.
They would have some community features like a tool library and food garden and a dog area, and individual indoor and outdoor spaces for everyone.
A portion of either the rent or sale price would be set aside for each person for financial advice or mental health support annually.
Ideally built by a combination of master craftspeople and trainees from at risk youth.