Is there a way to define a box around an equation in Pages using Latex?
Here is a option for drawing a box around formulae inserted into a Pages document.  This is not super elegant but could be what the OP is looking for.


From the Menu select Insert > Equation...
Enter the desired LaTex or MathML into the dialog box.


Insert a 'box'. Generally, a square shape sized, fill color removed or set to desired color, with a border of the desired width.
Align both so that the equation appears in the center.


It may be good to group them together option+command+G so they can be moved or resized together.





More info on LaTex or MathML for Pages: Pages version 7.1 (5683) inserting equations using LaTex or MathML.