The trade is control for capacity. In a shared kitchen you do the work, watch every batch and can change the recipe on a Tuesday. With a co-packer you hand over the process, buy output, and accept that changes cost money and lead time. What you gain is consistency, volume, and someone else’s equipment and quality system.
Settle five things before anything is scheduled: the minimum order quantity and what it does to your cash, who owns the recipe and the written specification, who sources and approves ingredients, who is responsible for shelf-life and testing, and whose licence the finished product is made under.
That last point has a clear answer in the rules. The Canadian Food Inspection Agency states that you need a Safe Food for Canadians licence if you are the last food business to manufacture, process, treat or preserve a food for export or interprovincial trade, and that a business whose sole activity is interprovincial trade does not itself need a licence but remains responsible for ensuring the food was handled by a licence holder. Whoever performs the last processing step is who the question lands on. Confirm your own case with the CFIA, and see the kitchen rental guides for the stage before this one.