No, you generally cannot apply to Ontario colleges without a high school diploma or equivalent *at the time of application*. While some colleges might allow you to *apply* conditionally, stating your intent to obtain your GED before the program start date, they will almost certainly require proof of completion of your GED *before* you can begin your college program.
In short, having a plan to get your GED is not sufficient; you need to have it in hand, or at least have official documentation showing you've passed the GED and received your certificate, before you can officially enroll and begin your studies. Contact the specific colleges you are interested in to confirm their policies, as they may vary slightly.