As you're probably aware, US immigration law applies differently to Canadians because they don't require visas for non-immigrant categories - except for categories that allow for potentially indefinite stays and that includes E. So the process of getting an E-2 visa is identical for Canadians as it is for citizens of any other country. You actually have to get a visa entered into your passports before you can enter the US.
This is another reason why E is more complex than other categories because you have to do the visa application, be interviewed by a consular officer (potentially, not always) etc.
There is no particular benefit to you in having Canadian citizenship in order to get an E visa, however I would still suggest you apply now for it as it can take over a year for the process to be completed, and it helps to have it because it's a far easier way to maintain the right to reside in Canada.
There is a bit of somewhat misleading information on the CIC website that says that a spouse of a Canadian citizen can maintain LPR status in Canada while living with with a Canadian citizen overseas, however what they fail to mention is that a claim of permanent residence makes you resident for tax purposes in Canada. However if you become a Canadian citizen, you can become non-resident for tax purposes (much like you're a British citizen but don't have to pay
taxes there). So although it's true, to do it on a long-term basis isn't very practical. I think you can take the oath at the Canadian consulate when they finally get around to it, you'd have to talk to CIC about how exactly it works for people going abroad.
Another thing to bear in mind is that an E visa is a non-immigrant category, eventually you will want to retire and stop the business - at that point you have to leave.
There is another category (EB-5) for immigrant investors, but you have to basically be minted to get in using that category, you need to invest a million dollars (or half a million in an economically deprived area) and employ at least ten US citizens or LPRs directly or indirectly (i.e. if you invested ten million, they'd consider you employ people at the bank to look after your money).
However in that category you get permanent resident status in the US.
Steve.