OK, so I'm going to try and engage with this seriously - and with a focus on hockey on the remote chance this thread doesn't get nuked from orbit.
It *is* extremely unlikely to ever happen. Back in the day two non-European countries applied to join the EU - Morocco and Turkey. Morocco was turned down flat - Morocco is not in Europe. Part of Turkey *is* in Europe however, so they were granted "candidate" status in 1999. In the year 2025 Turkey is not remotely close to joining the EU.
I would speculate that the reason Morocco and Turkey have been turned down is more cultural/ethnic than they are geographic, and that the EU secretly would be more open to Canada joining as we are a majority white/christian nation that speaks existing European languages (even as England/UK has left) - but to accept Canada would mean there's no reason not to consider Morocco and Turkey.
So what effect would it have on hockey? Well first and most simply joining the EU would mean joining the Schengen customs union. Europeans would have the full right to live and work in any EU country - so that would apply to hockey players playing in Canada. So no worrying about work visas.
As I think about it - I think that would mean opening up the CHL completely to European players, but might then restrict the number of US players in the CHL. European hockey leagues have restrictions on the number of Canadians they can employ IIRC.
The entire NHL salary cap could potentially be put at risk. I've been told there's a reason no Eurpoean league has a salary cap, and it has to do with European anti-trust laws - but even as a Canadian lawyer this is well beyond my knowledge.
And yes Canada would have to join the Euro. That would be a mixed bag. The Canadian dollar is tightly tied to the price of oil, which in turn if moderately tied to the Canadian economy in general. The price of oil goes up, the economy goes up, the dollar goes up. That means we can more easily buy things from abroad.
The price of oil goes down, the economy goes down, the dollar goes down. That makes it more expensive to buy from abroad - but that in turn encourages buying Canadian goods. It also encourages foreign companies to invest in Canada, which should eventually help the Canadian economy grow.
So having the Euro risks times where the Canadian economy is down, yet we have a high currency since it's no longer tied to the dollar. That could make the good times even better (good economy / low currency), but the bad times even worse (bad economy / strong currency).
Joining the Euro would have countless other effects - on dairy, food labelling, fisheries, environmental regulations - but that's well beyond hockey itself.