Danno, It is my understanding that the engine was the same between Antara & Captiva for the same year build.... but...... I do know that there was a gasket change on inlet manifolds and therefore other minor differences cant be ruled out.
If you have a 184hp (181 / 135Kw) and not the 161hp / 120Kw then if might be worth considering. (is there a returns policy?)
However........ before you purchase, you say the pump is "cutting on&off" . This implies it hasnt totally failed as such and I recall previous fuel pump discussions mentioning a corroded or defective terminal being the cause (often earths to chassis). Might be worth while exploring the earth and connector terminals first. It may be easier to simply create a new 'long cable' with alligator clips at each end and try clipping on different locations. This way you might be able to verify a defective supply in the existing.
The Advanced Search function might be worth exploring for discussions on this topic previously.