The Missouri River 340, planned for August 3-7, hasn't (yet?) cancelled. They're working out protocols for a social distanced version ... online safety briefing, masks while on shore, grab & go awards, etc. It sounds like they will run it if all of the relevant authorities (including the river!) fall in line. I'm signed up but will probably need to defer, given quarantine logistics for me and my partner (neither of us anywhere near Missouri).
Tough year for the race directors. The act of paddling is naturally socially distanced, unless you're drafting behind a war canoe full of opera singers, but it's hard to plan a large event without having a crowd form somewhere. For many of the participating organizations, like scout troops raising money selling food at checkpoints, it doesn't work without a critical mass of people. Even if you think you have it all worked out there's a chance that either a flare-up of the actual virus or an overabundance of caution from some official will torpedo the whole thing.