Technically it's illegal to participate in YC or any other accelerator on a tourist visa. You can do it, but you basically have to lie at the border. I know this is the case in the US and UK, possibly Canada as well. Unable to find the stories ATM, but I know I've seen a couple cases where YC founders were detained and then turned away for getting called out on falsified tourism claims at US border control. Seems like if they are going to start this kind of visa, they need a case that covers the earlier stage as well.

Don't even get me started on the double taxation you face if your business is successful as a foreign national.