If the Vikings had landed in a place with a milder climate and more hospitable natives...
Cortez was lucky to find a spot where he could land, plus colonization was made possible by their firearms (primitive as they were) which the earlier Vikings had not had.
Actually, there were precious few working firearms along with the early conquistadors. The Spanish military was still very much in the crossbow era.
The biggest advantage enjoyed by Cortez was to land among tribes with a bitter hatred for the Aztecs.