True, but still I think it's best to have the world cup in a single place. There are so many issues that appear when you host it in multiple countries, and also each country has it's own rules, and laws, visas, etc.
And at the end of the day most of the games will be played in the US anyway, so I'm not sure why Canada and Mexico wanted to be there. Maybe Canada wanted to finally be able to host it, but the other two already have done so in the past.
At least to me FIFA is giving a signal to other countries, they are basically saying we are not letting one of the most powerful countries around the world to hold the world cup on their own and they need to have partners to even have a chance to do it, and if any country wants to host the world cup on the future then they need to find partners as well in order to do so, so I think that from now on multiple hosts will become the norm and we will not see a single country hosting the world cup for a very long time.
I think that when it is hosted in a single country is better but usually FIFA has done so when the host country has some other countries near it that love football also,I remember in 2002 this was the case and the World Cup was held in Japan and South Korea and it had a lot of contention because of the referees favoring the host countries in a clamorous way,Italy lost 3-0 to South Korea something which was unimaginable until then.That is why I am more in favor when a single country is hosting the World Cup rather than holding it with other partners which can bring us to this non grateful situations where big teams are out of the play because of referees favoring home countries,it is much better when it is just one home country.