Image resize vs Image pyramid for generating ROI for pedestrian detection - OpenCV

For a OpenCV driving assistance application I want to generate ROIs as candidates for faster HoG classification of pedestrians. I'm running this on GPU. I do not want to use detectMultiscale function as it scan all over the image (including sky). Since the features are not scalable, which of the following functions I should use for resizing the images for generating the ROIs?

gpu::resize(const GpuMat& src, GpuMat& dst, Size dsize, double fx=0, double fy=0, int interpolation=INTER_LINEAR, Stream& stream=Stream::Null()) or

Image pyramids cv2.pyrUp(), cv2.pyrDown()

I couldn't find image pyramids in OpenCV GPU library(2.4.9).

Can anyone please suggest?

Thanks