Presumably, you will work with a post house or service bureau to get your animation onto HDCAM; you should check in with them about how they would want you to deliver the material. They might prefer your 1440x1080 image pillarboxed in a 1920x1080 raster.
I recommend using the "Scale Comp" script included with AE to get you started on your size change:
File > Scripts > DemoPalette.jsx > Scale Comp
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