Are glucose and galactose cis-trans isomers of each other?
Glucose and Galactose are best described as epimers of one another.
The three structures below all have the same molecular formula and the same connectivity, but differ in the absolute configuration at a single stereocentre (this is the definition of an epimer).
You can see that glucose and galactose are epimeric at the $\mathrm{C4}$ position, whilst glucose and mannose are epimeric at the $\mathrm{C2}$ position.


Image taken from Principles of Biochemistry, Lehninger et. al. (5 ed.)

To comment on the use of cis and trans.
The cis/trans nomenclature is used to describe the geometric isomerism of alkenes - it is not correct nor appropriate to use it in this context.  What you may be referring to is whether two adjacent stereo centres are syn or anti to one another.