Options to avoid a hard border are on the table, but they remain unpalatable to Theresa May's government.
Before CETA fully comes into effect, it must be ratified by each EU member state. Greece might have cause to stop it.
Lobster used to be a poor man's meal. Now it's the darling of foodies, and Canada's lobster producers are poised to cash in on sales to the European Union thanks to CETA.
It's likely that a future UK-EU trade deal will be subject to approval by all EU member states and their sub-national parliaments.
Britain has a number of bilateral treaties with Eastern European countries that will remain after Brexit.
The way that the EU dealt with its CETA trade deal with Canada makes it clear to Britain that negotiating a free trade agreement will be very long and difficult.
The CETA crisis will be resolved before long but the lessons of Wallonia point to a bigger European crisis.