Maybe a surviving independent
Kingdom of Galicia keeps its Portuguese holdings and expands south to the Algarve and maybe Leon and forms a mighty colonial empire like the OTL Portuguese did.
Portugal with Galicia and Leon (the two latters made the source of most of spain's oversea migrants) would have an insanely large settler population more than double that of portugal's IRL, it could simultaneously settle brazil, south africa and north america. Thanks to the colder, drier climate of the two latters compared to Brazil (where more than half of settlers died from illness in the first years of arrival), as well as the near limitless amount of land that would limit urbanisation the population will skyrocket, and all of this could happen in the early 16th century, a century before any succesful colonisation attempt were made in north america, a century at this time represented hundred of thousands of aditional settlers and 3-4 population doubling time in temperate, non tropical areas.
This has the potential to be much more than the portuguese, or spanish colonial empire ever where, this has the potential to have an entirely "portuguese-galician" Norht America, Brazil, Argentina, and, with time and lots of mixing, large part of subsaharian africa (at the very least below the congo). A country of 200,000 km² could have an empire controlling over 40 Millions km², and that today could have, together, population rivalling with china.
Actually a kingdom of galicia that just has galicia + portugal north of the tejo would have a lot of population pressure in the 15th century that could push many to further explore the atlantic until they discover and start fishing in north america, this small galicia+portugal (without the important early ports in algarve) may not be able to establish an empire in asia, and because of the fertile land in the azores and fishing ground in america the exploration could be more centered in the north atlantic rather than the south atlantic - african coast.
Portugal actually did settler colonies in madeira and the azores in the 15th century IRL, there if they do the same in north america, considering that most portugese migrant came from the north and galicia also was a huge source of oversea migrants, with a headstart in the mid 15th century the population cto ould eventually grow to tremendous size, by the time the french and english come in the early 17th century there would already be a few millions Galician-portuguese in norht america, and with this population they would quickly start expending west by the middle of the 17th century.
Population wise it would be equivalent to the early USA's by 1600 which wouldn't reach this population until 180 years later IRL. While it wouldn't get as much immigration as the USA got in the 19th century, pure natural growth along with the near endless farmland available would quickly make the population surpass portugal-galicia by the mid 17th century, and surpass that of any other european country by the mid 18th century, at this point they would likely have reached the west coast and you can expect additional portuguese-galician emigration thanks to a gold rush similar to the one in brazil IRL.
The result would be an entirely luso-galician speaking north america with a population of above 100 millions BEFORE the demogrpahic transition, it's unlikely it would have a significant industrial base, after all it's still portugal that colonized it, but by the modern days it could very easily have half a billion people maybe up to a billion, and control all of north america. All from a small kingdom of galicia that is even smaller than our portugal.