If you register the business as sole proprietorship, it's easier to file the tax. If your salary is low then you pay the regular tax rate. However, if your salary is high and your business is making profit, you will have to pay the higher rate of tax.
If you register the business as a corporation, you pay the corporate tax which could be lower, and you can hire your own family members who have lower tax rate to distribute the income among them. However, it's more complicated to file the tax.
You can still earn income while taking the EI, but your EI will be less as your income is more.