I will post here what I know, because I have always followed this issue of the 2026 World Cup.
Before FIFA confirmed the new format of the 2026 World Cup with 48 teams, we had unofficial news, but it appeared in various media, that Mexico and Canada would host 10 matches each.
Source
After FIFA's decision to have 12 groups of 4 teams, we still don't have official confirmation of how the division will be done, since now there will be 104 matches in total.
If it continues like this, with 10 matches in Mexico and Canada, that leaves 84 matches in the United States, it is very unbalanced.
In my opinion, the United States will host many more matches than the other two countries, but the 84-10-10 split is not good.
Maybe 64 games in the US and 20 in the other countries would be better.
If we consider the 16 stadiums of the World Cup, where there will be 11 in the USA, 3 in Mexico and 2 in Canada, we can get a better idea of this division.
I believe it is impossible for them to put many matches in Mexico and Canada.
I guess the reason of they chose Canada and Mexico to just help America with hosting the world cup is more sports facilities they have in America while in Canada and Mexico compared to America there are fewer good quality stadiums and hotels to host the world cup, also the main host is just America and since we have more countries on the world cup this time, two other countries will just help America.