Where to start an LLC owned by Canadian owners?
You really have your pick of the litter here.
If your business is tied to a particular state, for example if you are buying real estate or opening a physical store, your should form your LLC in that state.
Otherwise, go with one of the "corporate havens" - Wyoming, Delaware or Nevada. If you are expecting venture capital or serious investment in the near future, stick with Delaware. If you just want the best liability protection, low state fees, no state tax and easy maintenance requirements, Wyoming is way to go. Nevada is just as good as Wyoming, but a bit more expensive.