There’s more employees than just the border guards themselves. There’s the HR, the IT, Accountants, Legal etc etc. Block all of them. If those services are contracted out, ban their workers as well. Might be a bit troublesome with companies like Amazon or Microsoft, but since you’re banning individual workers rather than whole companies it might work out a little easier.

Make it so the deal is “If you associate with this company and you aren’t a Canadian citizen, you are personally not allowed to enter Canada”

At this point Canada should be playing hard ball. Ban all visas from anyone working for those companies, or anyone who delivers services to those companies for as long as they work for those companies. If they lie about who they work for, the ban is permanent and they personally are not allowed to set foot in Canada ever.