If my current employer uses a past criminal charge (which did not result in a conviction) while I was employed with a previous employer the reason to terminate me, is this not discrimination?

If your former employer is federally regulated, then it would be discrimination under the Canada Human Rights Act. If they are provincially regulated, then they cannot use the past criminal charge to terminate you for cause (i.e. without paying you anything), but they can terminate you on a "without cause" basis, as long as they provide you with the right severance. I would recommend reaching out to an employment lawyer at the number below to review your situation.