I have a pretty unique idea, but live in Canada. I want my company to operated and be registered in Canada. I am also a single developer, I have friends who are interested in helping, but they aren't team members(designer). I also can't think of a time when I've hacked something. Any thoughts?
Do we have to start a company in the US for you to invest in us?
Yes, but that's usually not a problem. It's easy for foreign nationals to start US companies (much easier than remaining here physically), and investors and acquirers prefer them.
Do we have to be US citizens?
No, as long as you can get here for at least three months. We've funded many startups founded by non-citizens.
Can you get us visas?
No, sorry, we don't do that. You'll have to figure out visas for yourself. If you know people from previous YC-funded companies who came from outside the US, we suggest you ask them for advice. They understand the options better than we do.
YC has a clear and openly stated bias for founding teams of 2<=X<=4 entrepreneurs.
Traction trumps MVP any day of the week. If people are already using your MVP, stress that. Traction is a commonly used de-selector.
The investor preference in SV is such that (it's likely) one of the first things required for a seed round will be some sort of DE or DE & CA incorporation. Since YC companies get funding, it's likely they'll require you to do the same. This is probably an area that if you choose not to give on where the company is incorporated, you'll turn off a lot of investors from SV. If it's a deal breaker for you, seek Canadian investment.
-Best of luck
In case you won't be accepted... At least you have tried.