The most important legal ramification of a Canadian launching a business in Silicon Valley is immigration. You must have a visa that allows you to operate the business (hire and manage employees, etc) in order to be running a business.
I started a business in Canada and was able to attract great Silicon Valley angel investors to invest in the Canadian corp. In the early-stages, there is less importance placed on where the business is domiciled than what the business has managed to achieve or who it's founders are.
There are significant advantages to keeping the business in Canada in the earliest stages and then moving to the Valley as you look to raise further funds and scale your business.
Without a doubt, it's good to be making frequent trips to SF & the Valley so as to build your network but from an actual formation perspective, I would argue that there are more benefits in the majority of cases to staying in Canada in the earliest stages.
Happy to talk to you about this in a brief call.
Best of luck!