england and spain had many colonies in the new world and each colony was administered by a governor who purchased (through money, favors or electioneering) privileges and authority. england had 20 separate colonies in the new world, as did spain. the french, dutch, portugese and russians also had colonial possessions.

note that canada and and the US are not the only anglo countries in north america. there are many more in the caribbean.

several of england's colonies banded together and fought a common war of independence, creating one big nation. the multiple canadian colonies were joined together by britain in order to make administration easier.

why then didn't spain centralize all of their colonial possessions into one nation? or why didn't the latin american independence movement gel into a pan-latin-american national movement?

there are a few things to consider. 1) the latin american world is much more populous and geographically diverse in the 18th century than the british american world. 2) spain had to maintain tight control over diverse aboriginal groups who vastly outnumbered the spanish. 3) there was very little inter-colonial spanish trafficking of goods, people or ideas. each colony operated more like a little enclave.

in the end it is a difference in colonial administration that explains the contrast between the big, consolidated anglo-american world and the scattered, diverse spanish-american world.

Edit: not sure how I sleepily and perhaps drunkenly failed to realize OP's question conflates two totally distinct concepts , both of which I articulate in my post: 1) why didn't the Spanish unite Latin America? 2) why didn't the Latin American independence movement created a singular Latin American nation?