To answer that question, Canada and Mexico aren't subsidiary hosts. They're co-hosts of USA this coming 2026, hence why their national teams did automatically got the advantage of being qualified directly. These 3 countries won the bid together, just like what happened in 2002 World Cup where Japan and South Korea hosted it together.
Well.. this is a difficult topic. I know that formally both Canada and Mexico are the co-hosts. At least on paper, they have the same rights as that of the United States. But at the same time, most of the matches are being staged in the United States and they are taking care of most of the expenses. So we can't say that in this case the status of the US is the same as that of the other two countries. However, I am not sure about the revenue distribution. IMO, revenues (apart from ticket sales) may be split equally between the three countries.
Since this is the first time the world cup has been hosted by three different countries, I guess FIFA should have come up with some new rules regarding how they are going to host this tournament, since this is the first time this has happened. Although these three nations do not have the same situation, there is no doubt that each country would like to host more matches because it will bring in more benefits, but I don't think it would be a good idea if one country hosted the main matches and other countries hosted fewer.
Folks, we're still in the year of 203, World Cup will commence somewhere in 2026 so that gives them a lot of time to prepare whatever is needed to make this world cup much better than the previous one which happened in Qatar. And since they still got three more years to prepare, let's expect that there will be some movement as the time passes by and maybe the list of matches and its venues will be updated officially in 2026. A lot will happen because the FIFA now have a new format where teams has been added as well as the games.