Wow, that’s a really hard Q and also a really important one. Here’s what I can tell u:

1. You can and must require the employee to self-isolate if he/she shows symptoms of COVID-19
2. If the employee has no symptoms but is at high risk due to being married to a pharmacist or health care worker or travel to a high risk area, they’re being advised BUT NOT REQUIRED TO self-isolate. Example: Public Health Agency of Canada  https://www.canada.ca/en/public-health/services/diseases/2019-novel-coronavirus-infection/health-professionals/national-case-definition.html
3. You can thus ENCOURAGE but NOT REQUIRE your employee to self-isolate
4. If you do try to force him/her to self-isolate, you expose yourself to liability risks, including constructive dismissal, breach of contract and discrimination on the basis of disability or perceived disabilty

Bottom Line: Self-isolation is, I believe, the right thing to do in this situation. And if there are symptoms, it’s also the legal thing to do. The problem is that without symptoms, the law isn’t on your side if you attempt to force him/her to self-isolate. But stay tuned. As the COVID-19 situation deepens, the public health recommendations are likely to change and require self-isolation for asymptomatic people at high risk. We’re just not there yet.
Thanks for the great Q, which, frankly, I think hasn’t gotten nearly enuf attention from the public health people. Glenn