If you are using contract shipping services, you will need to "transmit" shipments from time to time. You must do it after you have created a shipment and are ready to hand it over to Canada Post. Transmitting shipment triggers billing and sends shipping info to Canada Post.
Please only transmit shipments if you are sure they have been configured, packaged, and labeled correctly; you will not be able to void a shipment after that.
Here's how you transmit shipments:
Once you create a new shipment by clicking the Create shipment button on the order details' Shipments tab, the Transmit shipment button becomes available beneath the Shipping info section. Hit it, confirm the action, and the shipment will be transmitted.
Once a shipment has been transmitted, manifests' info is added to the Manifests section opposite the Shipping info section.
Here you can see the ID of the manifest that included the shipment. The "Document: Artifact" link allows you to save and print out the manifest without going to the CanadaPost manifests page.
A manifest is required so that Canada Post will bill you properly and accept your shipments readily.