The expression that logically completes the sentence would be; En Cancún, hace sol.
The meaning of the sentence
The above sentence mean that it is sunny in Cancun. Cancún has distinct wet and dry seasons. In the dry season which spans from November to May, "hace sol" is the most fitting response However, llueve may be used to describe Cancún during the rainy season.
Different seasons can be used to describe a territory and for Cancun, the above is the most suiting description.