Something like this?
I'm no linguist, so I couldn't really know how immigration would affect Colombia's Spanish. There are many loan words, due to a combination of anglophilia and, of course, immigrant populations adapting their words and expressions to their new home. Surnames have also been adapted - like, "Bell" being translated into "Campana" or Wang into "Reyes", "O'Hara" becoming "Ojara" or "Schneider" becoming "Eshnaider." Generally, Irish, English, Germans and Scandinavians are likely to either keep their surname or adapt it like this; Italians, Spaniards, French, Arabians keep their original surnames; and Indians, Chinese and Eastern Europeans adopt new Hispanic surnames. This, of course, is not a fixed rule or anything. Southern European generally move to cities and work in industry, in Caracas, Cartagena, Santafe, Hispaniola, etc. Spaniards, British, Arabs and Irishmen settle along the Magdalena, in the Southern Andes and the Venezuelan interior and become small farmers. Indians and Chinese settle along the coasts and become farm hands.
A factor to take into account is extensive mestizaje among the different immigrant population, with native Colombians and also with other immigrants. Immigrant communities remain small and generally integrate quickly into the mainstream, so that by the second generation most already only speak Spanish. Aside from cultural additions to gastronomy and celebrations, I think a slight difference in pronunciation could be observed - such as pronouncing l instead of r on account of Asian immigration.
Indeed. Also, I think my table reflects how developed countries' populations tend to grow - explosive growth at first, followed by slower growth after a demographic transition has been achieved.
My Gran Colombia, with a size of around 3,5 million square kilometers, would have a population density of 43 people per square kilometer. Just 3 people above OTL Colombia's density. It's true that it could support many more people, but as Nivek points out a lot of the territory would be inhospitable jungles. In any case, I think 150 million is a realistic estimate. And those resources will be much more developed due to Colombia bein stable, united and prosperous. Thanks for the information regarding the llanos though. I'll look into it...