If someone has a medical marijuana card, can they smoke in areas that don't allow smoking (for example inside restaurants or at work)? I'm curious about Vancouver, BC in particular.
The fact that you have a medical condition doesn't change the rules set by a private establishment or business.
A restaurant can bar all types of smoking (Including Vaping). Your medical condition would not be an exemption to this rule.
Your employer can have terms of employment that would prohibit you from smoking tobacco or even medicinal marijuana. So even thou you have a "doctors note", it doesn't change the fact that your job can randomly drug test you and subsequently fire you for testing positive for marijuana.
Furthermore, while many countries are relaxing drug laws and allowing for recreational and medicinal marijuana. Most still have stipulations that you must smoke it in private.
That card means that the person will not be arrested for smoking marijuana if they smoke marijuana. But they can get thrown out of a building for smoking if they smoke, and smoking marijuana is no exception.
If you need to smoke marijuana, then you need to do the same thing as someone who needs to smoke tobacco: Find a place where it is allowed to smoke.
The issue could come down to what the proprietor says, since the BC general law is limited to tobacco (Tobacco and Vapor Control Products Act, 2.1):
a person must not smoke tobacco, hold lighted tobacco, use an e-cigarette, or hold an activated e-cigarette
The medical marijuana law does not proscribe any particular mode or venue of consumption. Sections 3-7 only address legality of possessing and obtaining.
Since no law prohibits public consumption of medical marijuana, prohibiting a person with a medical condition from taking their medicine could be discriminatory. The Human Rights Act prohibits discrimination based on disability (and other characteristics); the case of P.G. v. Baton Rouge Restaurant is an application of that law. This limits the right of proprietors to govern conduct on their property, just as they may not discriminate in providing service to a person based on race, gender, sexual orientation or religion. Although there has been some call for specific laws addressing the matter, it appears that the strongest restriction is a recommendation from Health Canada that you not smoke marijuana in public.