How can I apply for the E-2 visa before my husband files for EB-5?

Yes — you may apply for an E-2 visa independently from your husband filing an EB-5 case, presuming you qualify, regardless of your husband’s future EB-5 filing. The E-2 and EB-5 are completely separate visa categories although the E-2 does not normally provide for dual intent, one does not prevent the other.
To qualify for E-2, you must be a citizen of a treaty country with the U.S. While you indicate that you are in Canada, you haven’t indicated what your citizenship is. Canada does have a treaty with the United States to allow Canadian citizens to apply for E-2 visa eligibility. The question then becomes one as to whether or not you will be applying based on your being an investor or otherwise an executive, manager, supervisor or essential employee of a qualifying treaty registered company.
You have two main options with respect to the filing of your E-2 versus your husband’s filing for the EB-5. Option A: Apply for E-2 now (before EB-5 is filed). This is generally the cleaner option as the E-2 requires you be able to demonstrate your intent to return to your residence overseas when your employment in the US pursuant to the E-2 is no longer required. This is known as “nonimmigrant intent” (temporary stay) whereas if your husband’s EB-5 is filed first, it shows that he at least has “immigrant intent”, which can then be impugned to you. While E-2 technically allows some flexibility, applying for E-2 after starting an immigrant petition can raise scrutiny.