Hello, you have many options as a Canadian entrepreneur moving to the US. If you are the major investor in your own company and own at least 50% of the company, you are eligible for an E-2 visa. If you already own a Canadian company and are opening a branch or subsidiary in the US you are eligible for an L-1 visa. If you are currently in the US as a student you may consider an H-1B visa. Regardless, of what option you choose you cannot just move to the US and start working. That said, you can make short trips to the US to set up your company without a visa, such as setting up bank accounts, signing legal documents, and agreeing to a lease.
Each of these visa options has its own timeline and various strengths and weaknesses. I am an immigration attorney in the US. I would be happy to discuss your options further with you on a call.
I'm happy to provide you the recommendation via private message. Your visa options will be based on your prior relevant experience and equity ownership of the Company.
Keep in mind that in *almost* every visa case, it's the US company petitioning the US Government on the immigrant's behalf. If you have too much control / ownership of the Company doing the petitioning, that can be problematic.
Happy to talk through my own experiences on this topic in a call. Or happy to simply provide you the reference via private message.
I hope this isn't coming too late but I recently went on a delegation with McGill University to SF. There is a program right now with the Canadian Trade Commission in partnership with Rocketspace, an accelerator there. If your company fits the characteristics on this page I believe you can be sponsored for a visa: http://www.tradecommissioner.gc.ca/eng/document.jsp?did=141342. Hope this helps!
You can find some generic advice online but you should ultimately get an immigration lawyer. Working with a larger company will make the visa situation easier as they have more resources- even Series A or later. It may be possible to sort it out as a founder, but that is likely more difficult (or at least expensive as I think the E-2 requires a significant investment). Some (eg, Skype, Zendesk) have founded the company in their home country and then moved to SF after they raised funding. If you have a special skill set (eg, PhD) there is also the O-1 visa.
Note: I am not a lawyer and this does not constitute legal advice.