one job would be full time, the other would be part time.
Can I justifiably within Canada work for two charities (but different audiences) and acquire rewarded as a fundraiser?
Sounds approaching a conflict of interest if you are being paid.
You would enjoy to disclose it to both companies. If they are ok with it there is no problem. There would be an issue if they be competing charities or if their major fundraisers were at equal time. Even if they're totally seperate and you don't tell your bosses, you could easily be fired when they find out.