Flagpoling as a US citizen

I’m a US citizen planning to flagpole next week to get my IEC open work permit. I’ve already been approved for it and all I should have to do is show up at the border. I’ve heard some conflicting information about flagpoling though. Apparently it’s still okay for US citizens to do so, but for many checkpoints an appointment is required? Unfortunately i missed the window to make an appointment at the big border crossings closest to Montreal. Does anyone know if i could just show up sans appointment at a smaller crossing like cornwall? It’s imperative that i do this next week, or I’ll most likely lose my job. Any help would be extremely appreciated thanks 😁😁😁