Yes, you can use the bonus attack action before or after the cantrip. That was explicitly clarified in the Rules answers: June 2016 -

Does the “when” in the Eldritch Knight’s War Magic feature mean the bonus attack comes after you cast the cantrip, or can it come before? The intent is that the bonus attack can come before or after the cantrip. You choose when to take a bonus action during your turn, unless the bonus action specifies when it must take place (PH, 189).

Probably after, but honestly, it doesn't matter

Sage Advice Compendium version 2.2 clarifies that the bonus action comes after:

Does the “when” in the Eldritch Knight’s War Magic feature mean the bonus attack comes after you cast the cantrip, or can it come before? The bonus action comes after the cantrip, since using your action to cast a cantrip is what gives you the ability to make the weapon attack as a bonus action.

However, it says the order can easily be reversed:

a DM would break nothing in the system by allowing an Eldritch Knight to reverse the order of the cantrip and the weapon attack

This complies with RAI, according to J. Crawford in the Rules answers: June 2016 -

Does the “when” in the Eldritch Knight’s War Magic feature mean the bonus attack comes after you cast the cantrip, or can it come before? The intent is that the bonus attack can come before or after the cantrip.

Generally you can choose the timings unless a description says otherwise:

You choose when to take a bonus action during your turn, unless the bonus action specifies when it must take place (PH, 189).