To bet against the Canadian housing market, for instance, you could look at shorting vulnerable financial institutions (Canadian banks and lenders with exposure to the Canadian housing market). You could also look at the Canadian dollar, which could conceivably fall if there's a housing crash.
Private startups are obviously a more difficult target, but you should consider that the types of events likely to push the private startup market into meaningful decline would in most cases also be bad news for publicly-traded tech companies as well, and you can short just about all of these. There are numerous advantages to targeting publicly-traded companies (liquidity, availability of information, in a major market correction there will be forced selling, etc.).