He is going to be King of Canada someday; which implies some interest to Canadians as he has significant (but limited) power as Canada's Head of State.

For example, the upcoming federal election could result in a number of possible coalitions. The new government will need the Queen's approval. In the future, it could be this guy making the call.

Also, the couple are coming here now (officially, but that could be a deception).

So you see, the wedding is of interest to Canadians for more than just the clothes. :-)

It isn't like I'm going to smoke an 80th to celebrate the marriage. It was a nice bit of theatre, and it'll be good for U.K. tourism.