There is no exact answer as it depends on your projected income profile, business risk, assets used in the business and your goals on repatriation of profits, not to mention any state issues. Compliance fees will be greater the more elaborate the structure is. The key is to remember is, will Canada under the treaty provide full foreign tax credit so there is no double taxation. Watch out for the LLCs as Canada treats them as corporations, not flow through entities, on venturing into the US.