You need to imagine a future where this ocean is populated and as active as all the other planet's coastlines.
That's more a perspective of the coming centuries then it is of the coming decades though. It's not like migration follows gradually and in line with each degree the temperature rises. Also in that scenario the temperature on the Pacific coast lines will likely rise much more then the temperature on the Atlantic coast lines because of the likely collapse of the AMOC (meaning the red line might even expand further south, perhaps making european migration away from the North Pole more likely then migration towards it).
If you compare the people of Canada and Turkey to the people of Ireland, obviously Canada seems easier to integrate. But if you compare the people of Canada and Turkey to that of Greece or Bulgaria, then it's much less obvious. The fact that Turkey has territorial disputes with Cyprus and Greece makes Turkey an unlikely member state, but culturally the people of Turkey (not the political system) are not that much less south-eastern European than Canadians are north-western European.
But i think practical ease of integration doesn't have to say much. If you look at 'compatibility' also Belarussians would make perfect candidates for integration, but even if they would want it the political reality doesn't allow it. Same has been long true for Northern-Macedonia joining, but in this case the blocking comes from inside forces rather than outside forces. And even where the political reality doesn't allow it, the people might not want it (e.g. Switzerland and Norway right now), the same could appear true for Canada (or Turkey) even if it doesn't seem like that today. If calculation are made, perhaps it might turn out Canada doesn't end up on the receiving ends.
Would Canadians also be interested in joining if it means increased taxes to pay for the benefits of people on the almost opposite side of the globe? Especially if countries like Morocco and Turkey join at the same time, argument will be made Canadians are paying for the development of those economies. Perhaps they will argue Canada is much better off as a strategic partner than a full-on member state, despite "its legal and cultural institutions grew directly out of European predecessors".
Either way, it has to be a two way desire, much like a friendship between two individuals. The reasons are less important than the desire. Both could become member for totally different reasons. One might join for economic benefits and the other for military strategic benefits for example, but in either way it in the end the European people (via their representatives) have to agree regardless. Again, the people of Ireland would likely be much more in favour of Canada joining than Greece or Bulgaria would be.