Geography.
Mexico lacks the natural resources necessary for great power status. The US has tremendous diversity of natural resources that yield great economic power.
Internal systems of communication and commerce: The Mississippi River system is critical to American success. It makes the interior of the nation (and all it's natural resources) accessible to major sea ports and sea lanes. River systems in the west also contribute to economic activity in the west. Mexico has no easy means to make the few resources it has as easily accessible as the US.
Diversity of population and means of movement: the US is closer to Europe and Asia than Mexico. It's physically easier to move from those two continents to the US than to Mexico, and that movement of people brings with it cultural and intellectual capital that Mexico simply can't.
The wealth of a nation lies in it's resources and people. If a nation can better utilize it's people and resources, it's going to be more powerful. The US did it, Mexico hasn't.
I also wouldn't call Canada a world power. It doesn't have the influence in any regard that the US, Russia, or China has. Those are really the only great powers anymore.